Inspection tool

ABSTRACT

This patent discloses an improved inspection tool for rapidly inspecting miniature electronic conductor patterns, circuits and the like. The tool focuses a laser beam to a small laser spot that raster scans a large conductor pattern area on the workpiece being inspected. Reflected laser light from the workpiece impinges upon a light detector that generates electrical signals according to the presence or absence of conductor pattern material on the workpiece at the momentary X and Y coordinate of the scanning laser spot. The light detector signals are compared with a previously encoded data image of the correct circuit pattern for the X and Y coordinates of the scanning laser spot. When the signals and the data agree at all X and Y coordinate points the workpiece is accepted. If the signals and the data do not agree at one or more X and Y coordinate points a defect in the circuit pattern is indicated. A defect may indicate out-of-tolerance dimensions, possible electrical short circuits, and/or open circuits. The extent of a defect may be determined by adjacent X and Y coordinate points and suitable computer programming, while workpieces having extended or out-of-tolerance defects are rejected. The improved disclosed inspection tool includes apparatus for automatically compensating for variations in the workpieces, and to effect registration for the scanning laser spot.

This is a continuation division, of application Ser. No. 592,154 filedJune 30, 1975.

SUMMARY OF THE INVENTION

The present invention relates to a rapid inspection tool for miniatureelectronic circuit patterns and more particularly relates to aninspection tool that uses a focused laser spot in a raster scan positionto momentarily illuminate spot areas of the workpiece being inspected.Reflected laser light from the workpiece activates a light detectorsignal generator. A computer retains a correct data image of theworkpiece and the light detector signals are compared with the correctdata image to determine the presence of circuit pattern defects.Workpieces having unacceptable pattern defects are treated as rejects.The invention includes means for automatically varying the X and Ycoordinate dimensions of the raster scan pattern whereby the raster scanpattern may be registered to variable X and Y coordinate dimensions ofthe workpiece.

STATE OF THE PRIOR ART

The inspection of miniature electronic conductor patterns has heretoforebeen primarily dependent upon the visual resolution of the human eye.

The most common inspection procedure for such circuitor conductorpatterns has been the use of visual resolution enhanced by a mediumpower microscope. The field of view of a medium power microscope isusually smaller than the workpiece being inspected, and thus theworkpiece or the microscope is usually moved several times to inspectits entire area for electrical short and/or open circuits. Handling andvisual inspection may take an experienced operator 5 to 10 minutes for a6 inch by 6 inch circuit pattern area. Dimensional inspection on amicrometer stage microscope may take another 5 to 10 minutes forinspection and recording dimensions.

Another inspection procedure has been the use of visual resolution withan image combining screen projector. In this inspection procedure, apositive image of the workpiece being inspected is combined andsuperimposed on a positive image of a correct workpiece. If the sizes ofthe two images are not identical a magnification adjustment is made.Registration adjustments superimpose one image on the other. Theinspection workpiece and the correct workpiece may then be alternativelyilluminated at about 10 cycles per second. Defects in the workpiecebeing inspected visually appear to flicker, thus the flicker draws theinspector's attention to the location of the defect and furtherevaluation of the defect can be made. This procedure is less fatiguingto the inspector than the microscope inspection technique and reducesinspection time somewhat, but such technique is subject to difficultiesthat limit its utility. For example, differential shrinkage between theX and Y coordinates of the workpiece being inspected may prevent asuperimposed image from registering with the correct workpiece image,and thus large areas may appear to flicker. Also, when a 6 inch squareworkpiece is projected at 4 power magnification onto a 24 inch squarescreen, short and open circuits 0.001 inch wide become only 0.004 inchwide on the screen and may escape visual observation.

Still another inspection procedure has proposed the use of visualresolution with a color television picture tube that combines the imagesfrom two TV cameras. This procedure would be visually similar to theabove described procedure except that the flickering of unusual colorcombinations may be used to indicate circuit pattern defects. Byelectronic circuit manipulation of one TV camera the black or dark, forexample, circuit pattern areas of the workpiece being inspected may beprojected by the picture tube as green areas, and the white, forexample, insulating areas may be projected as red areas. Similarly, witha second TV camera the black circuit pattern areas of the correctworkpiece may be projected as red areas, and the white insulating areasmay be projected as green areas. Thus when the images from the two TVcameras are combined, the green from the circuit pattern areas of theinspection workpiece plus the complementary red from the correct circuitpattern area combine and appear as white areas. Such will also occur forthe insulating areas where red from the inspection piece and green fromthe correct piece combine to produce white areas. In effect both thecircuit pattern areas together with the insulation areas over the entireworkpiece appear to be white. Against this white background shortcircuits in the inspection conductor pattern stand out as green areasand open circuits stand out as red areas. A cyclic camera scanning rateof about 10 frames per second provides a flicker to enhance visualobservation of such conductor pattern defects. The use of thisinspection procedure is not considered practical because of inadequateoptical resolution. American TV systems use a raster scan of about 530lines and even a 1200 line raster scan limits optical resolution toabout 6.000 inch/1200 = 0.005 inch. And optical resolution of 0.005 inch(or 200 lines per inch resolution) may be inadequate to detect defectssuch as electrical short and open circuits in the conductor patternwhere the defects may be as small as 0.001 inch wide requiring 1000lines per inch resolution.

One of the greater problems with inspection procedures that depend onmanual registration and visual resolution is that the inspectors tend to"go blind" after inspecting a few workpieces, and thereafter theinspectors may accept workpieces having electrical and dimensionaldefects.

The inspection tool of the present invention avoids the above describeddifficulties by providing mechanized workpiece handling and registrationtogether with laser optical inspection means having an automatedinspection resolution of about 1000 lines per inch.

The inspection tool includes coarse and vernier means for automaticallyincreasing and decreasing the dimensions of the tool's X and Yinspection coordinates thereby to match variable circuit patterndimensions caused by variable workpiece shrinkage which occurs becauseof prior processing of the workpieces. A part number reading devicescans an encoded part number on each workpiece and selects acorresponding correct data image from the computer data bank forphotocell signal comparison. A marking means applies encoded markings toa margin of the workpiece indicating acceptance, or the location andtype of a rejection defect. A preferred configuration of the tool mayinspect 36,000,000 points over a 6 inch by 6 inch conductor pattern areato an accuracy of 0.001 inch. Modified configurations may inspect a 12inch by 24 inch circuit board pattern to an accuracy of 0.002 inch, or a31/4 inch diameter silicon wafer pattern to an accuracy of about 0.00035inch.

OBJECTS OF THE INVENTION

In view of the above, it is a principal object of the present inventionto provide a novel, integrally packaged, inspection tool which mayfunction with integral and/or associated electronic computer means.

Another object of the present invention is to reduce the handling andregistration time of a workpiece being inspected by providing mechanizedhandling and registration for the workpiece.

Still another object of the present invention is to provide means in theinspection tool for compensating for variations in the X and Ycoordinates of the workpiece being inspected. Another related object ofthe invention is to provide gross and vernier adjustments of the X andthe Y inspection coordinates of the inspection tool which compensate forvariations in coordinates of the workpiece being inspected.

A further object of the invention is to provide a laser raster patternto illuminate the workpiece being inspected and means for receivingreflected laser light from the workpiece being inspected to determinethe presence and absence of conductor pattern material on the workpiece.

A still further object of the invention is to compare the abovereflected signals from conductor pattern material to previously encodedand correct data image signals in the computer memory bank wherebydifferences between the reflected signals and the correct data imagesignals may indicate a defect in the conductor pattern material.

Yet another further object of the invention is to provide registrationmarks and patterns on the workpiece being inspected and light or photodetector means for reading and interpreting the registration markswhereby the X and Y adjustable coordinate grids of the inspection toolmay be adjusted to match variable X and Y coordinates and registrationmarks of the workpiece being inspected.

Other objects and a more complete understanding of the invention may beobtained with reference to the specification and claims taken inconjunction with the accompanying drawings wherein:

THE DRAWINGS

FIG. 1 is a fragmentary schematic perspective view illustratingapparatus constructed in accordance with the present invention forscanning and inspecting workpieces.

FIG. 2 is a fragmentary schematic and elevational view illustrating partof the apparatus shown in FIG. 1 and showing laser optical pathsrelative to the workpiece being inspected.

FIG. 3 is a fragmentary schematic front elevational view of theapparatus shown in FIGS. 1 and 2 and the laser optical paths in FIG. 2from the front;

FIGS. 4, 5 and 6 are fragmentary schematic views in plan showing severalexemplary forms of workpieces that may be inspected in apparatusillustrated in FIGS. 1-3;

FIGS. 7A and 7B are enlarged fragmentary plan views of portions of atypical workpiece pattern, for example, an unsintered ceramic greensheet and a sintered ceramic green sheet;

FIG. 8A is an enlarged fragmentary plan view of a small corner portionof the workpiece illustrated in FIGS. 7A and 7B and illustrating typicalelectrical circuit defects such as electrical shorts and opens, prior tolamination and sintering.

FIG. 8B is an enlarged fragmentary plan view of a small corner portionfor another typical workpiece, such as may be used for circuit designand layout purposes and after stacking, lamination and sintering;

FIG. 9 is an enlarged fragmentary sectional view taken along line 9--9of FIG. 7;

FIG. 10 is a representation of the acceptable location of the conductorpattern corner outlines as represented by a locus of dots, that may bewithin maximum dimensional tolerances for stacking and laminating.

FIGS. 11 through 16 are schematic illustrations of several exemplaryworkpieces which even though distorted, may be assembled for stackingand laminating.

FIG. 17 is an enlarged fragmentary view of one corner of a workpiecewith a registration pattern taken thereon and from FIG. 4;

FIG. 18A is a schematic front elevational view of a portion of theapparatus illustrated in FIGS. 1-3, and showing the portion in a homo orrest position;

FIGS. 18B and 18C are fragmentary sectional views taken respectivelyalong lines 18B--18B and 18C--18C of FIG. 18A;

FIG. 18D is a schematic representation of pulse waveforms produced bythe laser beam passing over the grating; and representing suitablepractical voltage waveforms after rectification and differentiation;

FIG. 18E is a fragmentary plan view of a portion of the apparatus whichis modified to permit the location of a starting point for synchronousoperation;

FIG. 18F is a schematic representation similar to that shown in FIG. 18Dbut with respect to the portion of the grating shown in FIG. 18E;

FIG. 18G is a schematic block diagram of the electrical circuitryemployed to give a meaningful output from the photocell associated withthe apparatus shown in FIG. 18A;

FIGS. 19 and 20 illustrate the portion of the apparatus illustrated inFIG. 18A in alternate positions;

FIG. 21 shows the apparatus of FIGS. 18-20 with a frame and associatedvernier means for altering the position of the apparatus;

FIG. 22 is an enlarged fragmentary schematic view of means for grosslyaltering the slope of the frame and apparatus shown in FIG. 21;

FIG. 23 is a fragmentary perspective view of a portion of the laseroptical system with means for vernier alteration of the Y coordinates;

FIG. 24 is an end view of a portion of the means of FIG. 23.

FIGS. 25 and 26 illustrate the vernier effects on the Y coordinatesoccasioned by the rotation of the means 24;

FIGS. 27 and 28 are fragmentary perspective views similar to FIG. 23 andshowing the compensation for skew positions of the workpiece;

FIG. 29 is a fragmentary schematic view showing means that may beemployed for gross adjustments and alignment of the Y inspectioncoordinates;

FIG. 29A is an end view of the apparatus shown in FIG. 29;

FIG. 30 is a fragmentary perspective view illustratingelectro-mechanical means that provide vernier drive for the scanninglaser and workpiece feed;

FIG. 31 shows a focused laser spot and approximate energy distributioncurves thereof relative to, for example, pattern lines on the workpiece;

FIG. 32 illustrates a laser spot and photocell response curve andvoltage patterns corresponding to spot position on a line pattern.

FIG. 33 shows a spot pattern position relative to a line or lines beforeand after employment of the apparatus of the present invention, and;

FIG. 34 is a fragmentary schematic perspective view in block formillustrating the operation of the apparatus of the present inventionwith a computer.

GENERAL DESCRIPTION OF THE INSPECTION TOOL

Referring now to the drawings and particularly to FIGS. 1, 2 and 3thereof, a workpiece 1, being inspected by the inspection tool of thepresent invention, moves from left to right in the direction indicatedby the motion arrows 2. The workpiece 1, described in more detailhereinafter, is approximately aligned with the inspection tool byaccurately located sprocket holes 3 within the left margin 4 and edge 5of the workpiece 1. Less accurately fitted sprocked holes 6 within theright margin 7 and edge 5 of the workpiece 1 may be employed forhandling and interaction with conveyor drive or guide mechanism (notshown). As shown, the workpiece 1 is positioned on the surface 8 of acylinder 9 with the sprocket holes 3 engaging left sprocket teeth 11 inthe cylinder that are designed for an accurate fit in the left sprocketholes 3. The right sprocket holes 6 may have clearance when they engagethe right sprocket teeth 12 in the cylinder 9.

A coherent light source, in the present instance, laser 14 projects anapproximately collimated beam of laser light 16 onto a rotatingmulti-facet mirror 17. The mirror 17 is supported by and rotated by ashaft 18, which in turn is driven by a first motor 19. The rotation ofthe multifacet mirror 17 reflects and sweeps the beam of laser light 16across an optical surface of a first lens 21. Each facet of themulti-facet rotating mirror 17 serves to reflect and sweep the laseroptical axis or beam 25 through a continuous angle as shown by dottedlines 23 and 24-26 in FIG. 3. The lens 21 may be arranged to focus thereflected laser beam 16 to a laser spot approximately 0.001 inchdiameter continuously on the surface of the workpiece 1 in a work zoneduring the sweep of the laser optical axis through the angle 23-26. Forillustrative purposes the rotating mirror 17 is shown with 8 facets, butit actually may have up to 18 or more facets and the motor 19 may rotateat 6000 or more revolutions per minute. Likewise for illustrativepurposes, the lens 21 is shown as a two element cemented doublet, but itactually may employ multiple elements arranged along the laser opticalaxis before and after the rotating mirror 17.

As shown in FIG. 2, a partially reflecting mirror 27 intercepts andreflects a portion of the laser light being swept (see FIG. 3). Thelight from the mirror 27 is then reflected on to a grating 28 having aplurality of interdigited light receiving and light transmitting linesthereon. A more detailed description of the X coordinate registrationfunction of the grating 28 is set forth hereinafter. The reflectedportion 29 of the sweeeping beam 25 intercepts the lines of the gratingat an oblique angle as the beam is swept across the work zone. As shownin FIG. 2, the reflected portion 29 is focused to a spot about 0.001inch diameter at and along the swept surface of the grating 28. Thegrating 28 allows portions of the sweeping laser light beam 29 to passthrough light transmitting portions of the grating and a second lens 31focuses this light on a first light detector means 32, in the presentinstance a photocell. A major portion of the laser light sweepingthrough the angle 23, 24 and 16 passes through the partially reflectingmirror 27 and a flexible prism 33 to become focused to a 0.001 inch spotat and along the surface of the workpiece 1. Subsequent paragraphsprovide more detailed descriptions of the Y coordinate registrationfunctions of the flexible prism 33. Diffused and reflected laser lightas indicated by the arrow 34, is reflected from the 0.001 inch focusedlaser spot sweeping the workpiece 1, and a portion of this diffused andreflected laser light 34 enters a transparent light conductor rod 35.One or more second light detector means or photocell signal generators36 located at one or more ends of the transparent light conductor rod 35pick up and convert a portion of the reflected laser light 34 intoelectrical signals to indicate the presence or absence of differentlines on the workpiece.

As shown in FIG. 3, a fully reflecting mirror surface 37 on a smallprism 38 intercepts a portion of the angular sweep at 23 and 24 of thelaser beam 25 being swept through the angle 23-26. The interceptedportion 23 and 24 of the sweeping laser beam 25 is reflected by themirror surface 37 in a direction indicated by dotted reflection line 39to a third light detector means or photocell signal generator 40. Themirror surface 37 and the small prism 38 may be manually adjusted toleft or right and may be useful for adjusting and defining the leftintersection 42 of a laser beam spot with the workpiece 1. A rightintersection 43 and the scan line 42 and 43 on the workpiece 1 mayrepresent the useful portion of the sweeping laser scanning spot as thespot is swept across the workpiece 1. The intersections 42, 43 may beconsidered to be the end points of the laser beam axis lines 24 and 26respectively as the rotating mirror 17 sweeps the laser ray axis linethrough the angle 23, 24, and 26.

It is to be understood that the elements of the inspection tool of thisinvention may be positioned, adjusted and journaled for cooperatingspatial relationships approximately as shown by the drawings in asuitable frame or chassis (not shown).

THE WORKPIECE(S)

A brief description of the workpiece(s) 1 and associated FIGS. 4 to 16may provide a better understanding of the various features of theinspection tool of the present invention. At the outset it should beunderstood that the workpieces may take any of a number of forms and theone described hereinafter is utilized to indicate a worse casecondition.

The workpiece 1 may be initially formed from a casting slurry thatincludes about 95% powdered alumna and about 5% powdered glass as solidsmixed with a liquid that includes a plastic monomer and a volatileliquid vehicle. The slurry is poured on a plastic transport web andpasses under a wide "doctor blade" that regulates the thickness of thecast slurry to about 0.013 inches. After the solids settle and thevolatile liquid vehicle evaporates the workpiece material 1 reduces to along and/or continuous web about 0.008 inches thick. After or duringfurther drying and/or stabilizing, the plastic transport web is strippedoff and may be cleaned and reused for another slurry casting. At thispoint in the processing sequence, the web of workpiece material 1 may beinverted such that the bottom smooth side that was formerly in contactwith the plastic transport web is on the top side, the left and rightedges 5 and the sprocket holes 3, 6, and/or the alignment holes 53, 55may now be mechanically punched to the configurations of FIGS. 4 and/or5.

Via holes 58 (FIGS. 7 and 8) about 0.006 inches diameter may be piercedthrough the workpiece 1 using mechanical punching, electron beam, laserbeam and other means. The via holes 58 are formed at predeterminedlocations and may be filled with suitable electrically conductivematerial as well as patterns on the surface of the workpiece 1. One suchsuitable electrically conductive material might include powderedmolybdemum, a plastic monomer, and a volatile liquid vehicle, mixed toform a paste that may be screened or otherwise suitable applied to theworkpiece 1. It should be noted that forming of the via holes 58 in theworkpiece 1 may distort the integrity of various dimensions of theworkpiece. Likewise the Application of the pattern of electricallyconductive material to the workpiece 1 may distort various dimensions.As will be more fully explained hereinafter, several features of thisinvention have been directed to detecting out-of-tolerance distortion ofvarious dimensions of the workpiece 1. After the Application of apattern to the workpiece 1, and drying, the workpiece may be ready forinspection by the inspection tool of this invention.

As shown in a preferred configuration in FIG. 4, the workpiece 1 to beinspected may be one or more parts of a long and/or continuous web 43 ofmaterial having one or more adjacent workpieces 1. When one or moreworkpieces 1 are present on the long and/or continuous web 43, long dashlines 44 represent the shearing and/or separation points for and/orbetween the individual workpieces. Accurate sprocket holes 3 andregistration marks 45 may be located in the left hand margin 4 of theworkpiece 1. Note that sprocket holes 3 (and teeth 11, FIG. 1) may beomitted at positions 46 as indicated by black dots near the left end ofthe separation line 44 for purposes of aligning the workpieces 1 withthe rotational position of the cylinder 9. Machine readable part numbers47 may be encoded in the leading marginal edge 48 of the workpieces 1.The part numbers 47 may be either suitable combinations of lines andspaces or the like and/or suitable groups of perforated holes, whicheveris most convenient for previous processing operations. In a like manner,locational registration marks 49 and the clearance sprocket holes 6 maybe located in the right margin 7 of the workpieces 1. A conductorpattern area or like pattern area to be inspected may be generallywithin the short dash outline 50.

FIG. 5 shows another configuration for the workpieces 1. Here theworkpieces 1 may have been previously separated along the lines 44 (FIG.4) and then located on and/or bonded to a web of flexible material 51.For example, the web 51 may be composed of stainless steel, fiberglass,and the like and may include apertures 51 somewhat larger than theoutlines of the short dash lines 50 so that the inspected pattern areamay be punched out of the workpiece 1. The workpiece 1 in thisconfiguration may optionally have accurately located alignment holes 53located near the left top and bottom corners. The web of material 51then may have accurately located alignment pins 54 secured to the weband closely fitting the alignment holes 53. Alignment and handling holes55 near the right top and bottom corners of the workpiece 1 may haveclearance to corresponding pins 56. Other numerals in the configurationof FIG. 5 provide essentially the same functions as previously describedrelative to FIG. 4.

FIG. 6 shows still another configuration for the workpiece(s) 1. In thisinstance the workpiece(s) 1 may be a rigid glass plate bonded to acarrier 57. Other numerals in the configuration of FIG. 6 provideessentially the same functions as previously described relative to FIGS.4 and 5. Note that in the workpiece configurations of FIGS. 4, 5 and 6,the areas to be inspected are generally defined by dash outlines 50. Thedash lines 50 may enclose an area of about 24 inches by 12 inches forcircuit patterns on circuit boards made of fiberglass epoxy and thelike; or may enclose an area of about 6 inches by 6 inches for patternson unsintered ceramic material and the like. The diameter of the focusedand raster scanning laser spot is preferably approximately proportionalto the length of the X coordinate scan line, i.e., for a 12 inch widefiberglass board and pattern, 0.002 inches; and for a 6 inch widepattern on ceramic 0.001 inches. Thus, widths larger than 12 inches orsmaller than 6 inches may be inspected with proportionately sized rasterscanning laser spots.

FIGS. 7A and 8A show larger scale plan view portions of two among manytypes of various patterns that may be inspected on the surface of anunsintered ceramic material or workpiece 1. In this instance, thesurface of the workpiece 1 within and/or adjacent the dash lines 50 maybe partially or wholly covered by patterns similar to FIGS. 7A or 8Aand/or a combination thereof. Patterns such as FIG. 7A and/or the likemay be known as "circuit line", "interconnection" and "fan-out" planepatterns. Patterns such as 8A and/or the like may be known as "ground"and "voltage" plane patterns.

The circuit pattern 59 of FIG. 7A may be formed of powdered conductivematerial, such as molybdenum paste, about 0.006 inches wide and 0.0012inches thick. The circuit lines 59 may run horizontal, vertical, or atvarious angles in and/or on the surface of the workpiece 1. The circuitlines 59 may be independent and/or interconnected with other circuitlines and/or "caps" 60. The caps 60 may be about 0.007 inches diameterand may be used as interconnectors to circuit lines 59 and/or via holes58 and to aid in proper filling of line 0.006 inch diameter via holeswith conductive material such as molybdenum screening paste. Planarconductors 61 of FIG. 8A may be about 0.0012 inches thick, of driedmolybdenum screening paste covering small and/or large areas on thesurface of workpiece 1. Doughnut or oval shaped insulating areas about0.017 inches across may be positioned at suitable locations within theplanar conductor 61 surrounding screened caps 60 and filled via holes58. The caps 60 may provide interconnections between filled via holes58, circuit lines 59, and planar conductors 61 wherever interconnectionsmay be required by the circuit design.

The above described dimensions may be considered as applying only tosmall portions of a pattern on a workpiece 1 to be inspected, such asmay be illustrated by FIGS. 7A and 8A. Over a large portion of theworkpiece 1, small dimensional errors and/or defects may be cumulative,resulting in overall workpiece patterns that may have larger dimensionsthan nominal dimensions. Thus, for manufacturing and assembly purposesplus (+) and minus (-) limits to nominal dimensions may be establishedto avoid electrical short and/or open circuits due to cumulativedimensional errors. Manufacturing experience has indicated thatexpansion or contraction of a circuit pattern due to cumulative errorsfrom via hole piercing and/or circuit pattern Application, may beapproximately linear within and/or near the outlines of dash lines 50(FIGS. 4, 5 and 6). The cumulative dimensional errors may have, mosteffect near the corners of a pattern area. Thus while the patterns ofvarious workpieces 1 having the same part number may be geometricallysimilar, each workpiece may have slightly different dimensions for thecorner locations of the dash lines 50 due to cumulative dimensionaland/or shrinkage and/or expansion errors. For inspection purposes,nominal dimensions based on previous manufacturing experience may beassumed together with plus (+) and minus (-) deviations from nominaldimensions so that a plurality of workpieces may be assembled insuperimposed relation without causing additional errors. The inspectiontool includes means that are adaptable for inspecting such geometricallysimilar patterns having nominal dimensions together with (+) and minus(-) dimensional deviations thereof. However, for practical assemblypurposes, the deviations at the corners of dash lines 50 for unsinteredceramic patterns may be limited to ± 0.001 inch X and/or Y tolerancedeviations by the design of the patterns such as shown in FIGS. 7A and8A and as explained hereinafter. Thus the inspecting tool may includemeans for inspecting and accepting patterns having nominal dimensionsand geometrically similar patterns having ± 0.001 inch deviationstherefrom at the corners, and rejecting patterns exceeding ± 0.001 inchtolerance deviations.

The inspection process for dimensions, electrical short circuits andopen circuits, etc. is described in more detail in later paragraphs. Itshould be mentioned here however, that a marking device(s) 70 (FIG. 1)may be activated and arranged to place appropriate markings in the righthand margin of the workpiece 1. Visible and/or machine readable markingsin a suitable code by the marking device(s) 70 might indicateinformation such as: A = accept, R = reject, S = short circuit, O = opencircuit, + or - = ± non-acceptable dimensions, and other codedinformation. In general, error and/or dimensional markings such as S,O, + - etc. may be placed in the right hand margin near the laser scanline that has detected such errors during inspection. Such locations forS and/or O markings may assist in locating these pattern errors ifmachine and/or manual correction of the error(s) is required. The Aand/or R markings may be placed near the lower right hand corner of theoutline dash lines 50 following the inspection of the workpiece 1.

After inspection, the inspection accepted and/or a marked workpieces 1may be separated from their transport web and planar stacked one aboveanother in layers of 5 to 30 or more workpieces 1. Each workpiece 1 mayhave a different part number and a different conductor pattern but theyall should be within acceptable ± dimensional tolerances for stackingpurposes. The correct vertical stacking alignment (one above another)may be provided by electro-optical-mechanical automation (not shown)and/or the mechanical use of long alignment pins (not shown) fitting thesprocket holes 3 (FIG. 4) or the alignment holes 53 (FIG. 5).Preferably, each successive layer of stacked workpieces 1 should berotated 90° relative to the layer under it during stacking to equalizeshrinkage factors in later process operations.

When the stacking operation has been completed the stacked layers ofworkpieces 1 may be laminated under heat and pressure. During thelaminating process the plastic monomer 10, the work sheets becomesplastic and polymerizes to bind the stacked layers of work sheets 1together into a rigid (unsintered) planar structure that may be removedas a unit from the laminating fixture (not shown). During properlaminating there may be little or no significant changes in the planardimensions of the workpieces 1, but the thickness of the stackedassembly of work sheets may be reduced considerably under the laminatingpressure. However, an exception to "no significant change in planardimensions" has been noted: The ends of an open circuit in a planarmolybdenum conductor pattern that may be separated by 0.001 inches orless may be frequently squeezed together in a planar direction by thelaminating pressure, thereby changing the open circuit to an acceptablepattern without an open circuit.

FIG. 9 illustrates the ± dimensional tolerance limitations that may befollowed by the designer of unsintered circuit patterns such as areshown in FIGS. 7A and 8A. FIG. 9 is a vertical cross section through agroup of laminated workpieces 1 taken through molybdenum paste filledvia holes 58, their caps 60 and circuit lines 59 (see FIGS. 7A and/or8A) for reference locations near the upper left corner of dash lines 50(FIGS. 4, 5 and 6). A nominally dimensioned workpiece layer 63 is shownlaminated to a 0.001 inch wider workpiece layer 64 above layer 63 and a0.001 inch narrower workpiece layer 65 below layer 63. It may beobserved that the filled via 58 and their caps 60 provide adequateinterconnections when stacked in the described sequence. However, when a0.001 inch narrower than nominal workpiece 65 is stacked above a 0.001inch wider than nominal workpiece 66, the center lines of theserespective via holes 58 and caps 60 may then be offset by as much as0.002 inch. As such electrical interconnection between the filled viahole 58 of layer 65 and the cap 60 of layer 66 may still be adequate butthe cap 60 of layer 65 (in center column of via holes and caps as shown)may come as close as 0.0035 inches to the via hole 60 at locations 71(near left column of via holes and caps). A 0.0035 inch separation isabout the minimum of safe insulation separation for stacking designpurposes considering that vertical stacking tolerance in the stackingoperation add another ± 0.0005 inch of misalignment tolerances betweenlayers 65 and 66. The cumulative stacking tolerances might thus improveinsulation separation to 0.0045 inches or reduce the insulationseparation to as little as 0.0025 inches. A line pattern area layer suchas layer 72 generally causes less spacing problem areas than areacontaining caps such as caps 62. Similar conditions may also occur nearthe other three corners of the dash lines 50. Larger workpieces may haveproportionately less dense patterns and use larger dimensionaltolerances, and smaller workpieces with denser patterns may use smallerdimensional tolerances. However, for a 6 inch square workpiece area suchas previously described and illustrated relative to the corners ofoutline dash lines 50, a manufacturing and/or use tolerance in X and/orY of ± 0.001 inch from nominal dimensions may provide useful trade-offs.In the above instance a ± 0.001 inch tolerance in X and Y dimensions maybe a compromise among various conflicting factors, such as a circuitdesigners desire for a denser circuit patterns and a manufacturersdesire for high production yields (resulting from wider insulatingspacings and few internal short circuits in the stacked assembly ofworkpieces 1 as shown in FIG. 9). Thus the inspection tool should beadaptable to accept nominal pattern dimensions up to 6 inches square butalso ± 0.001 inch deviations in geometrically similar patterns, andrejecting patterns exceeding the ± 0.001 inch deviations that may occurin the corners of the dash lines 50 (FIGS. 4, 5 and 6). The nominalcorner location is shown by the (circled) dot 73 in the center of FIG.10. Various X and/or Y locations for the extreme ± 0.001 inch cornerslocations of the outlined dash line 50 are shown by 8 surrounding dotssuch as a dot 74 each, up to ± 0.001 inch in X and/or Y from the nominalposition of dot 73. Thus considering cumulative tolerances the cornerlocations overall from top left corner to top right corner of 50 may beoverall ± 0.002 inches but not exceeding 0.001 inches from nominal inany one corner of the dash line pattern outline 50 in the X coordinatedimension. Likewise the top to bottom pattern of corners in the 50outline may be as much as ± 0.002 inches overall but not exceeding ±0.001 from nominal in any one corner in the Y coordinate dimension. Thecircle around dot 73 is not actually present, but the circle is usedhere to distinguish a nominal corner location 73 from other possiblecorner locations indicated by dots such as 74 that may be otherwiselocated up to ± 0.001 inch in X and/or Y coordinates from the nominallocation 73. The effects of such dimensional tolerances on the sizes andshapes of patterns to be inspected may be made more apparent by a briefdescription relative to FIGS. 11 to 16.

In FIGS. 11 to 16 the sizes and shapes of nominal patterns to beinspected may be shown by the dash lines 50 as previously described. Thelight solid lines 75 may show the outlines of a few of the otherpatterns having dimensions other than nominal. The corners of the otherthan nominal outlines in FIGS. 11 to 16, as may be formed by the solidlines 75, should occur within ± 0.001 inch in X and/or Y coordinatesfrom nominal corner locations. When the corners of lines 75 comply withthe above corner tolerance dimensions any of solid line 75 patterns orthe dash line 50 patterns of FIGS. 11 to 16 may be stacked one aboveanother after inspection as previously described. The vertical sectionFIG. 9 also shows the effects of ± 0.001 inch tolerances in stacking.The outlines 50 and 75 of FIG. 11 show geometrically similar outlines.However, the shrinkage and/or expansion of the workpiece 1 may beslightly different along X and/or Y coordinates resulting in otheroutlines 75 such as in FIGS. 12 to 16 that may not be exactlygeometrically similar to the nominal outlines 50. These other outlines75 may be acceptable for stacking and laminating assembly purposes whenthe corners of the outlines 75 are within ± 0.001 inch in X and/or Y ofthe nominal corners of the outlines 50. Thus the inspection tool shouldbe capable of inspecting the workpiece(s) 1 having patterns within theseother outlines 75. In some instances these other outlines 75 may beskewed in X and/or Y directions as shown in FIGS. 14 to 16, but sincesuch workpiece(s) 1 might be stacked and laminated satisfactorily theinspection tool should be capable of inspecting them.

As an aid in the alignment and registration of the inspection tool tothe pattern areas to be inspected on the workpiece(s) 1 registrationpatterns 76 such as shown enlarged in FIG. 17 may be accurately locatednear the pattern areas (see also FIGS. 1, 2 and 3). Among many shapesthat may be used for registration pattern purposes the shape shown inFIG. 17 may be convenient to use since its design corresponds to opticaldefinition and/or resolution patterns and may also be used as such. Thethree vertical lines 77 of FIG. 17 may be 0.006 inches wide with 0.006inches spacing between them. The three horizontal lines 78 may be 0.006inches high with 0.006 inches spacing. The vertical and/or horizontallines may be 0.030 inches long. A preferred location of the registrationpatterns 76 (FIGS. 1, 2 and 3) may be in margin areas outside thepattern outlines 50 and/or 75 of work sheet 1. The locations of theregistration patterns 76 may be the same relative to all the otherpattern outlines 50 and/or 75 of patterns to be inspected except forproportional shrinkage or expansion of the workpiece 1.

Preferably the registration patterns 76 may be applied to the worksheet1 in a fixed dimensional relationship to the outlines 50 and/or 75 ofthe conductor patterns. The registration patterns 76 may be applied inthe same operation simultaneously with the applications of conductorpatterns within the outlines 50 and/or 75 on the worksheet(s) 1. Withthis simultaneous application of patterns any subsequent shrinkage orexpansion of the worksheet may cause concurrent and correspondingdimensional changes for both the registration patterns 76 and thecircuit patterns within the outlines 50 and/or 75. By applying tworegistration patterns, one near the upper left corner and the other nearthe upper right corner of outlines 50 and/or 75, an X-coordinatemeasurement between the two corner registration patterns may be comparedto the dimensions of their nominal positions to determine theirdimensional deviations from nominal. Such dimensional deviations mayoccur from shrinkage or expansion of the workpiece 1. Thus thesemeasured deviations may then be used in calculating correspondingdimensional deviations for the upper corners of the pattern outlines 50and/or 75 without actually measuring the corner locations. A similarprocedure using a lower pair of separated registration patterns may beused to calculate dimensional deviations for the lower left and rightcorners of the pattern outline 50 and/or 75. Likewise Y-coordinatedeviations from nominal locations may be calculated by measuring thedimension between a pair of Y-coordinate separated registration patternsmight be respectively located near the left upper and lower corners, orthe right upper and lower corners of the pattern outlines 50 and/or 75.Additionally, dimensional shifts and/or skews of the registrationpatterns 76 relative to the left sprocket holes 3 (FIG. 1) orregistration holes 53, 54 (FIG. 5) may be used to calculate thecorresponding shifts and/or skews of the circuit pattern outlines 50and/or 75. Multiple registration patterns in X and/or Y coordinatelocations may be used to enhance deviation measurements. In summary, themeasured deviations of the registration patterns from nominal may bemeasured and used by the inspection tool to align and register thetool's laser raster scan pattern to various patterns being inspected asmay be understood from later descriptive paragraphs.

Now that the subject of dimensional deviations from normal has beendescribed for a worksheet 1, some of the causes for such dimensionaldeviations may be explained. The worksheet material may be constantlyshrinking at a diminishing shrinkage rate as the curing time increasesdue to progressive evaporation of its original liquid casting vehicle.Thus if the worksheet 1 is made from different lots of worksheetmaterial that have been made at different time periods the individualworksheets as made from such different lots of material will havedifferent shrinkage rates prior to stacking assembly. Additionally, themolybdenum paste composition of circuit patterns applied to theworksheets includes a liquid vehicle. A portion of this liquid vehiclemay evaporate but also a portion of the liquid vehicle may be absorbedby the worksheets and result in an expansion of the worksheets. Amongthe different circuit pattern designs some patterns have a greaterpattern density on the workpiece than others (compare FIG. 8A with FIG.7A) and thus require more molybdenum paste. Such denser patterns mayprovide more liquid vehicle to be absorbed and increase the expansion ofthe worksheet relative to less dense circuit patterns. Then while thecircuit patterns are dried to evaporate most of the liquid vehicle, someof the vehicle evaporates from the worksheet material and the worksheetmay start to shrink again. From the above explanation of some causes fordimensional deviations it may be understood that the workpiece 1 isconstantly subject to some type and/or types of dimensional changesprior to inspection of the circuit patterns by the inspection forexcessive dimensional changes while other worksheets may deviate fromnominal but may be acceptable for stacking assembly purposes providedthat such deviations do not exceed ± 0.001 inch from nominal dimensionsin X and/or Y coordinates.

In order to detect dimensional deviations from nominal as small as ±0.001 inch the size of the inspection tool's scanning laser spot maypreferably be about 0.001 inch diameter. This diameter of the scanninglaser spot may also enable the inspection tool to detect typicalelectrical short and/or open circuits as small as about 0.001 inch wide.Referring back to FIGS. 7A, 8A, such typical short circuits 79 andelectrical open circuits 80 are shown in the circuit patterns and may beclassified by the inspection tool as electrical defects and be rejected.Defects smaller than about .001 inch wide may be detected down to awidth where photocell signal response becomes lost in an environment of"noise" signals. Such smaller width short circuits, if previouslyundetected during inspection may occasionally be "blown" after sinteringby passing a high current through them thereby eliminating the shortcircuit. Likewise such open circuits may become closed circuits duringlaminating where the laminating pressure may squeeze the ends ofmolybdenum conductor paste together. Wider electrical defects may bedetected and rejected by the inspection tool. The detection ability of a0.001 inch scanning laser spot may be dependent on the percentage areaof the spots laser energy that may be reflected by the surface of thewhite worksheet or absorbed by the black circuit pattern areas that havebeen applied to the white worksheet. Accordingly, the detection abilityof a scanning laser spot may be useful to detect the edges of largerconductor circuit lines to about 1/8 the diameter of the laser spotbefore the photocell response signals become obscured by the electrical"noise" of the detection system. The detection ability of a laser spotis described in more detail in later paragraphs.

As a general summary of typical workpieces defects it may now beunderstood that substantially all of such typical defects may bedetected by a scanning laser spot about 0.001 inch diameter as used bythe inspection tool. After inspection the accepted workpieces arestacked, laminated and sintered.

THE SINTERING PROCESS

The sintering process may be described as a separate topic because ofthe large dimensional change that may occur as the laminated workpieces1 are sintered. During sintering the material of the unsinteredworkpieces and their conductor patterns coalesce and their dimensionsmay shrink by about 17.2% ± 1.5%. The sintering process converts thealumna particles etc. of the laminated sheets into a vitrified alumnaceramic. The molybdenum particles of the circuit patterns duringsintering, convert and bond to each other into continuous conductorcircuit lines of metallic molybdenum. Insulating spaces betweenconductor circuit lines are preserved as insulating spaces in thevitrified ceramic. In the sintering process the laminated workpieces areplaced on, for example, a flat alumna tile and then heated in a suitablehigh temperature furnace in a hydrogen atmosphere at about 1600° C forabout 24 hours. After cooling, the top and bottom of the rigid ceramicplate or substrate is then inspected by the inspection tool in a mannersimilar to the inspection of a rigid glass master plate (see FIG. 6).However, for this type of inspection the rigid plates are preferably fedinto the inspection tool in a manner such that the action line of theinfeed is tangent to the top of the cylinder 9 (FIG. 7) to avoid bendingand/or breaking the rigid plates. Likewise the grating 28 may be changedto provide a more suitable dimensional reference that may accomodate thenew dimensions resulting from the 17.2% shrinkage that occured duringsintering. A comparison of FIG. 7A and 7B or FIGS. 8A and 8B may beuseful in understanding the significance of the 17.3% shrinkage; FIGS.7A and 8A represent the size of unsintered workpieces 1 while FIGS. 7Band 8B are representative of the sintered ceramic. For illustrativepurposes FIGS. 7A, 7B, 8A and 8B have all been drawn to the same scale.It may be noted that the circuit designers prefer the dimensions of thesintered sizes (FIGS. 7A, 8A) in making circuit layouts since it is thesintered size that is used to fit with other components of a largerassembly such as a computer. Thus, the designer's drawing may show thesintered size of a circuit pattern (FIGS. 7B, 8B) but the inspectiontool may inspect the unsintered worksheets 1 (FIGS. 7A, 8A). As will bemore fully understood hereinafter, it may be convenient for theinspection tool to use two different dimensional reference gratings 28;one grating based on an 0.005 inch X-Y design grid spacing for sinteredceramics and another grating based on an 0.006 inch X-Y grid spacing forunsintered worksheets. It should be noted however that either gratingand /or grid spacing may be used interchangeably depending on which ofthe grid spacings is preferable for sintered and/or unsinteredinspection by the inspection tool.

THE GRATING

In accordance with one feature of the invention, the grating 28 (FIGS.1, 2) is used to provide a basic dimensional reference for theinspection tool. By controlled manipulation of the grating theX-coordinate dimensional reference may be proportionately contracted orexpanded to correspond with the shrinkage or expansion of the dimensionsof the worksheet 1.

To this end the grating alternately absorbs and transmits light energyto the photocell 32 as the reflected beam 25 sweeps the grating, thealternating presence and absence of light on the photocell creating apulse form voltage output therefrom, the number of pulses of whichproviding a precise location of the beam 25 as it traverses theworkpiece 1. Several types of gratings may be employed, in the preferredembodiment the grating includes a plurality of interdigitated oralternate opaque and transparent lines extending over a portion of asubstrate, in the present instance a rectangle of transparent glass orother transparent material. An equivalent grating may include alternatenonreflecting and reflecting line surfaces extending over an area of asuitable supporting material such as a smoothly polished ceramicmaterial. In this instance the photocell would be placed to receive thereflected light transmission.

As heretofore described, the partially reflecting mirror 27 (FIGS. 1, 2,3) is used to divide the sweeping laser beam 25 into two synchronouslymoving beams with a major portion of the laser energy being focused on aworkpiece 1. The partially reflecting mirror 27 thus reflects a portion29 of the sweeping laser beam 25 as a focused laser spot to the grating28. The spot may sweep across the grating in a straight sweeplike 81-82as shown in FIG. 18A, FIGS. 18B and 18C show portions of the grating 28taken near the respective left and right sides of the grating. Opaque ornon-reflecting grating lines 83 and transparent or reflecting lines 84of the grating 28 are arranged preferably at a 45° angle to thesweeplike 81-82 and laser spot 25. The alternating grating 83, 84 may beaccurately formed across the grating 28 by photographic or othersuitable means and preferably each line is 0.001 inches wide as measureddiagonally along the scan line 81-82. Thus the actual width of the lines83, 84 may be 0.001 inch x sin 45° as measured perpendicular to their45° slope. The grating 28 is preferably about 7 inches wide in order toassist in the inspection of a 6 inches wide area of the worksheet(s) 1as outlined by the dash lines 50 (FIGS. 4, 5 and 6). The above describedarrangement may provide about 7000 grating lines across the grating 28at 45° to the sweeplike 81-82, with one half of the alternating lines83, 84 absorbing energy from the sweeping laser spot and the other halfof the lines being transparent for laser light transmission purposes.The light energy from a focused laser spot about 0.001 inch diameter maythus be alternately absorbed and transmitted by the 45° grating lines83, 84 as the spot sweeps across the grating along the sweep line 81,82. The light energy of the sweeping laser spot is essentially constantas the spot sweeps along the sweep line 81, 82 but the opaque ornon-reflecting lines 83 dissipates this constant laser energy while thetransparent or reflecting lines 84 allows transmission of laser energyin pulses. The pulses of transmitted laser energy may be focused bysuitable optical means, for example, the lens 31 (FIGS. 1, 2) or amirror (not shown) to the first photocell 32. The photocell 32 thenprovides electrical pulse signals corresponding to the laser pulsetransmitting lines 84 of the grating 28.

After suitable electrical amplification, and referring now to FIG. 18G,the output pulses from the first photocell 32 correspond to the upperportion of FIG. 18D where voltage V is the ordinate and the abcissarepresents an X-coordinate corresponding to the traverse sweep of thelaser spot 85 (FIG. 18B) along the sweep line 81-82. The voltage peaks86 have broad tops and correspond to laser light transmission lines 84of the grating 28. The valleys 87 have broad bottoms and correspond tono laser light transmission by the energy dissipating or opaque lines83. The slope lines 88 between the peaks 86 and the valleys 87 are steepand correspond to a voltage transition as the laser spot 86 traversesthe boundaries between energy absorbing lines 83 and energy transmittinglines 84, or vice-versa. By conventional differentiating circuit means(not shown) the amplified photocell signals, as shown in the upperportion of FIG. 18D, may be differentiated and rectified to appear assharp peaks 89 as shown in the lower portion of FIG. 18D. Preferably thesharp peaks 89 may correspond in X-coordinate alignment with the steepslopes 88. In this manner the sharp peaks 89 provide accurate electricalmarking signals as the sweeping laser spot 85 traverses the transitionzones between the lines 83, 84 of the grating 28. Then by electricallycounting the number sharp peaks 89 that may occur from a givenX-coordinate starting point as the laser spot 85 sweeps across thegrating 28 the momentary location of the sweeping laser spot 85 may bedetermined by the sum of the count. Since the transitions along thesweep line 81-82 for the grating lines 83, 84 occur every 0.001 inch thecounting means provide location data for the laser spot at 0.001 inchintervals over a grating width of, for example 6 to 7 inches. Thus forexample, a count of 347 may be the equivalent of 3.474 inches from thestarting point. Smaller intervals using interpolation means, describedlater, may be used for large and/or small measurements that may occur atand/or between the sharp peaks 89. An X-coordinate starting point forcounting purposes may be provided on the grating 28 by omitting one ormore energy absorbing lines 83 (FIG. 18E) and using a wide energytransmitting lines 89 near the left margin of the grating. The photocellresponse to the wide energy transmitting line 89 is a broad voltagepulse 90 (FIG. 18F) that the electrical system may recognize as thestarting point by its difference from the normal pulse 86. Electrically,a time delay latching circuit may be used to recognize the longer timeduration of the broad pulse 90 which the latch initiating the countingcircuit on the adjacent down-swing 88 of the photocell response. Insummary, the grating and its sweeping laser spot may provide accurateX-coordinate data for the momentary location of the sweeping laser spoton the grating, and since the grating sweeping laser spot and theworkpiece sweeping laser spot are synchronously aligned with each other,the X-coordinate data of the grating sweeping laser spot may be used todetermine the momentary X-coordinate of the workpiece sweeping laserspot and thereby to obtain dimensional or positional data relative tothe workpiece.

As has been described previously, circuit patterns on a worksheet 1(FIGS. 4, 5, 6) that may nominally be 6.000 inches wide in theX-coordinate may vary up to about 0.001 inches at any of the 4 cornersof the broken outline 50 (FIGS. 10 to 16) due to shrinkage or expansionand have proportionate displacements of the circuit patterns betweensuch corners of the outline 50. In order to inspect a shrunk or expandedpattern the inspection tool may function initially to determine thewidth of the pattern by measuring a width between the left registrationmark 45 and a right registration mark 49 and then function to adjust theinspection tool's nominal measuring and/or inspection system to coincideand/or register with the shrunk or expanded circuit pattern dimensions.Means for initially determining the width of the pattern are describedin later paragraphs.

Several approaches may be used for adapting the inspection tool'snominal measuring system to the shrunk or expanded worksheets. A complexapproach is to take nominal counted X-coordinate dimensions from thelaser sweep of the grating 28 and use a computer to multiply the nominaldimensions by the shrinkage or expansion ratios of each worksheet toobtain new X-coordinate dimensions. An example of this approach mayillustrate the complexity: Assume that a nominal 6.000 inch dimensionhas been measured by the tool and found to be actually 5.9993 inches dueto shrinkage; then each of the 6000 nominal X-coordinate points alongthe laser sweep line should be multiplied by the ratio 5.9993/6.000 toobtain new dimensions, which then requires "rounding out" to the nearest1/8 mil or about 0.0001 inches. Since there are, in the present example,6000 sweeplines for a 6.000 inch length of worksheet and a new worksheetis to be inspected every few seconds this requires 6000 × 6000 =36,000,000 multiplications by the 5.993/6000 ratio and another ratioevery few seconds. Such a multiplication effort requires a large andexpensive computer.

A simpler and preferred approach to obtain new dimensions adapted forshrinkage or expansion is to provide the grating 28 (FIGS. 19, 20) withthe equivalent of a pivot point 91 near the left side of the grating andthen to suitable depress (FIG. 19) or elevate (FIG. 20) the right sideof the grating to adapt the grating measurements to the shrunk orexpanded dimensions of the workpiece(s) 1. In illustrating thisapproach, consider that in FIGS. 18A, 19, 20 only 2 of the 6000 or moreactual grating lines on the grating 28 are shown: lines No. 0 and No.6000. The sweeplike 81-82 may intersect the No. 0 line as the pivotpoint 91 and the No. 6000 line at 92. Then with the grating 28 in thenominal position of FIG. 18A and the grating 28 the counting system maycount 6000 indicating a nominal dimension of 6.000 inches betweengrating lines No. 0 and No. 6000 as previously described. In the nominalposition of the grating 28 as shown in FIG. 18A the inspection tool usesthe grating for accurate measurement purposes between the left and rightregistration marks 45, 49 of the worksheet(s) 1 (FIGS. 4, 5, 6). Ifwhile making such measurements a nominal dimension such as 6.000 inchesis found to be actually 5.9993 inches due to shrinkage, the grating 28is rotated downward about the pivot point 91 (FIG. 19) whereby the newintersection 93 of scan line 81-82 with the grating line No. 6000 is notapproximately 0.0007 inches higher (to the left and above) than theprevious intersection 92. Since the grating lines are at 45° (FIG. 18B)to the scan line 81-82 this 0.0007 inch higher intersection point 93also results in the intersection point 93 being moved substantially anequal 0.0007 inch distance to the left (tan 45° = 1.0000). Thus thenominal dimension of 6.000 inches between points 91, 92 (FIG. 18A) isforeshortened by 0.0007 inches thereby becoming 5.9993 inches betweenpoints 91, 93 in FIG. 19. The sweeping laser spot 85 (FIG. 18B)traversing the grating 28 (FIG. 19) now results in a count of 6000X-coordinate points between locations 91 and 93 with all X-coordinatepoint dimensions reduced proportionately by the ratio 5.9993/6.000 tomatch the shrinkage of the workpiece 1. This is without the complexcomputer ratio calculations required above.

FIG. 20 illustrates a similar procedure wherein the nominal grating ofFIG. 12A and point 92 may be rotated upwardly about the pivot point 91to provide an increased dimension between the scan line 81-82interceptions 91, 94 with the grating lines No. 0 and No. 6000, andthereby match an expansion of the workpiece 1. In summary the sweepinglaser spot and the nominal position of the grating provide a basicdimensional reference scale for accurate measurement of work sheetdimensions and pattern position and if such work sheet dimensionsdeviate from the nominal dimensions the effective scale may then beshrunk or expanded to match such work sheet deviation dimensions by asuitable rotation of the grating about a pivot point.

The above described ability of the sweeping laser spot and the gratingto shrink or expand the inspection tool's measuring scale is also usefulin inspecting workpieces after stacking and laminating. As heretoforedescribed the green sheet, during sintering incurs a 17.2% dimensionalshrinkage. For subsequent assembly purposes and the conveniences of thecircuit designer, the sintered dimensions are considered to be the basicdimensions and the drawings of individual workpieces show these sintereddimensions. Additionally, the basic sintered dimensions (FIGS. 7B, 8B)may be designed to a basic 0.005 inch X-Y grid matrix 95, 96 having X-Ysub-grids of 0.0005 inches. The basic matrix allows the via holes and0.005 inch wide circuit pattern lines to be centered on basic grid linesand the edges of circuit pattern lines to be on the sub-grid matrixlines. The circuit pattern, as is conventional in the industry may bedesigned by a suitably programmed computer wherein electrical circuitdata is fed to the computer and a computer controlled drafting machinethen make a large scale drawing of the circuit pattern. A data image ofthe circuit pattern may be retained by the computer memory bank,magnetic discs. However for unsintered worksheet inspection purposes thebasic sintered dimensions may be expanded to compensate for sinteringshrinkage and the worksheet then inspected to the actual unsintereddimensions. If for example the sintering shrinkage were found to be17.2% then the basic sintered dimensions may be 100% - 17.2% = 82.8% ofthe linear length of the workpieces inspection dimensions. Thus if thedata image width of a sintered circuit pattern were to be retained inthe computer memory bank as 5.000 inches then the worksheet inspectiondimension for this width would be 5.000/.828 = 6.0386 inches. Since this6.0386 inch dimension is so close to an even 6.000 inch dimension thenominal grating of FIG. 18A may be rotated about the pivot point 91 toelevate the 6000the grating line by 6.0386 - 6.0000 = 0.0386 inches asin FIG. 20. This large or gross adjustment may provide a new inspectionscale of 6000 X-coordinate inspection points covering the full 6.0386inch width of the workpiece. There may now be a simple ratio of6000/5000 = 1.2 to the sintered design dimensions retained by thecomputer memory bank. The computer may then multiply its retained dataimage of a circuit pattern by 1.2 to obtain expanded X-coordinates forworksheet inspection purposes. This arrangement has a further advantagein that the basic 0.005 inch X-Y grid matrix used for sintered designpruposes may now become a 1.2 × 0.005 = 0.006 inch X-Y grid matrix 97,98 for inspection purposes shown in FIGS. 7A, 8A. The centers of viaholes and the center lines of circuit lines may then be conveniently on0.006 inch matrix grid lines with the edges of circuit lines aligningwith 0.001 inch sub-grid lines.

It should be understood that the dimensions of the workpiece beinginspected by this procedure have not been changed but only that therotation of the grating has provided a suitably expanded measuring scalethat may now allow the use of the convenient 0.006 inch X-Y matrix grid.The expansion of the measuring scale in the example was in effect by theratio of 6.0386/6.000 = 1.00644. Then with the computer expanding a5.000 inch wide sintered pattern by a factor of 1.2: 5.000 × 1.2 ×1.600644 = 6.0386 inches wide for unsintered workpiece inspection.Additionally, small adjustments of the grating may be used to compensatefor up to ± 0.001 inch variations of worksheet pattern widths aspreviously described.

FIG. 21 shows the grating 28 together with associated structural andactuating components. The grating 28 may be retained in a light or lowmass sub-frame 99. In the illustrated instance several small pivotblocks 100 are spaced about and attached to the sub-frame 99 at suitablelocations for coaction with knife edge pivots. One end of knife edgepivot blades or links 101 engage the pivot blocks 100 and the other endof the knife edge pivot blades 101 engage suitably located pivot blocks102, 103, 104, 105, 106, 107 as shown. As shown, the pivot blocks 102,104, are attached to spring elements 108, 109 which are fastened to arotating frame 110 with fastening screws 111, 112 and the other end ofthe spring elements 108, 109 contact adjustable set screws 113, 114 inthe frame 110. The pivot blocks 103, 105, 106 and 107 are attachedrespectively to grating actuator means 115, 116, 117, 118. The actuatormeans may be various types of components that produce physical motion ordisplacements responsive to electrical, hydraulic, air pressure, etc.signal commands. Among such components responsive to electrical signalcommands may be piezo-electrical devices, magnetostrictive elements,solenoids, etc. However, for this Application the actuators 115, 116,117, 118 are preferably piezo-electrical devices because of theirrelatively fast motion response to command signals and low powerconsumption. As illustrated, the actuators 115, 116, 117, 118 arefastened to springs 119, 120, 121, 122 respectively with these springsbeing fastened and adjustable to the grating rotating frame 110 in amanner similar to the springs 108, 109 by using fastening screws andadjustable set screws. The springs are used to maintain compressionforces on the knife edge pivot blades or links 101 and thereby avoidbacklash or lost motion. The adjustable set screws provide smalldisplacements for the springs and may be used for initial gratingadjustments and calibration purposes.

As has previously been described relative to FIGS. 18A-18E, the sweepinglaser spot traverses the grating 28 along the sweepline 81-82, of the6000 or more alternating opaque and transparent grating lines positionedat 45° to the sweepline 81-82, only line 0 and line 6000 are shown inFIG. 21, it being understood that there may be grating lines to the leftof 0 and to the right of the 6000 grating line. As shown, the lines 0intersects the sweepline 81-82 at a point 91. The knife edge pivotblades or links 101 associated with pivot blocks 102, 103, 104 near theleft end of the grating are used, in the present instance, to effect apivot point located at 91 for small rotary motions of the grating in thevertical plane. The small rotary motions may be applied to the gratingby the actuators 118, 116 located above and below the intersection 92 ofthe scan line 81-82 with the No. 6000 grating line near the right end ofthe grating. As described previously relative to FIG. 18A, 18E, 19, 20 a± 0.002 inch vertical motion at the right of the grating has a neteffect of ± 0.002 inches in the distance between the intersection points91 and 92 with the laser scan line 81-82 since the scan line remains ina fixed spatial position while the grating moves and pivots about thepoints 91.

The grating 28 of FIGS. 18A, 19 and 20 includes means whereby thegrating may be physically moved to the left or the right byapproximately ± 0.001 inch. This physical movement of the grating thenallows the X-coordinate mesuring points of the grating, such as thesharp peaks 89 of FIG. 18D, to be aligned or registered to the workpiecepattern that is to be inspected, or for initial machine to optics andworkpiece registration. To this end, the grating may be physically movedhorizontally to the left or right by actuators 115, 117 which therebyprovide improved alignment or registration between the grating 28 andthe workpiece 1 to be inspected.

The entire grating rotating frame 110 and components attached theretomay also be rotated about the pivot point 91 to obtain larger rotarymovements of the grating 28 then may be obtained from actuators 118,116. To this end, to obtain such larger rotary movements the leftportion of the rotating frame 110 incliudes machined arcs 123 andgrooves 124 to form an arcuate track having a center on the pivot point91. Ball bearings 125 or the like engage the arcuate grooves 124 toposition the rotary frame 110 and permit rotary movement thereof. Thebearings 125 are supported by a main frame plate 126 that includes alarge aperture (not shown) substantially coextensive with the gratingand includes means therein supporting the second lens 31 of FIGS. 1, 2.The larger rotary movements of grating rotating frame 110 may beobtained by vertical movements of a spring link member 128 attachedthereto by a fastener 129 at the lower end of spring. The upper end ofthe spring may be attached to one half of a spring loaded lead screwsnut 130 by a fastener 131 as may be seen more clearly in FIG. 22.

The actuating means for obtaining large rotary movements of the gratingrotary frame 110 (FIG. 21) may be seen in FIG. 22. A small stepping-typemotor 132 rotates a lead screw 133 and an encoding disk 134 attachedthereto by a nut 135. As shown, the stepping motor 132 is supported byan extension 136 of the main frame plate 126 (FIG. 21). The rotation ofthe lead screw 133 moves a spring-compressed split nut 130, 137vertically upwards or downwards thereby moving spring 128 attachedthereto. A pair of screws 138 straddle the lead screw 133 and extendthrough the split nuts 130, 137 to compression springs 139 andadjustable nuts 140 whereby an adjustable compression force may beapplied to the split nuts to reduce backlash. A light source may bearranged to project light through the encoding disk 134 to multiplephotocells 142 whereby the rotational position of the motor 132 is knownand its rotation controlled to start at a predetermined position. Themotor encoding disc, light source and photocells are availablecommercially and an equivalent magnetically controlled package may besubstituted therefore. The arrangement described relative to FIG. 22enables an inspection tool operator or a computer to make large or grossrotations of the grating 28 of FIG. 21 to a desired positioncorresponding to an average or nominal shrinkage factor of the workpiece1; the actuators 118, 116 may then adjust the grating to the shrinkageor expansion of an individual workpiece 1.

THE FLEXIBLE PRISM

The elongated flexible prism 33 of FIGS. 1, 2, 3 may be used to provideY-coordinate adjustments for the laser beam 25 as the beam sweeps alongan X-coordinate line on the workpiece 1 by refracting the beam 25. TheY-coordinate adjustments assist in the alignment and/or registration ofthe sweeping laser beam 25 to the workpiece 1 being inspected. To thisend FIGS. 23-28 illustrate functions of the flexible prism 33, the prism33 being composed preferably of optically transparent semiflexibleplastic material such as polyvinyl chloride or the like and positionedto overlie the work zone adjacent the workpiece. In FIG. 23 the laserbeam 25 is shown being swept through sweep angle 24-26 passing throughthe nominal position of the prism 33 and interceptong the workpiece 1along an X-coordinate nominal line 143-144. In FIG. 24 it may beobserved that the top and bottom surfaces of the prism 33 are parallelto each other and in this nominal position are also perpendicular to theplane of the sweep 24-26 of the sweeping laser beam 25, and thereforethe beam 25 passes through the prism without deflection in theY-coordinate. however, by suitable means to be described later the prism33 may be rotated clockwise or counter clockwise about its long axis145-146. A counter clockwise rotation from the nominal position isillustrated in FIGS. 26 and 27 wherein the laser sweep plane 24-26 thatenters into the rotated prism 33 emerges from the rotated prism as sweepplane 147-149 with both sweep planes deviating from the perpendicularangle of FIGS. 23 and 24 by entrance and exit angles equal to theangular rotation of the prism. The optical properties of the rotatedprism 33 may be such that the emerging laser sweep plane 147-149provides a beam 148 which may be parallel to the entering sweep plane24-26 but separated therefrom by a small Y-coordinate dimension -ΔY, thebeam 148 intercepting the worksheet 1 along a new sweep line 150-151.Similarly a clockwise rotation of the prism 33 as shown in FIG. 25 mayprovide another sweep line on the worksheet 1 that is parallel to thenominal sweep line 143-144 but separated therefrom by the dimension +ΔY.For small rotational angles of the prism 33 the Y-coordinatedisplacement dimensions -ΔY and/or +ΔY may be considered to beproportionate to the angle of rotation of the prism. Thus in conjunctionwith suitable sensing and control means as described hereinafter bysmall rotations of the prism 33 the nominal scan line 143-144 may bedeflected to align or register with the X-coordinate positions of theX-coordinate lines on a workpiece 1 that may have become displaced fromnominal positions as previously described relative to FIGS. 11, 12 and13.

The flexible material of the prism 33 may permit the prism to be twistedabout its long axis 145-146 as shown in FIG. 28 and/or rotated about itslong axis as shown in FIG. 27. Such twisting may be accomplished, forexample, by rotating the right end of the prism 33 counter clockwise andthe opposite or left end of the prism clockwise as shown in FIG. 28. Theemerging sweep plane 152-154 of the beam 153 from the twisted prism 33may be skewed (not parallel to the entering sweep plane 24-26 and theskewed sweep plane may now intercept the workpiece(s) 1 along a skewedsweep line 155-156. In FIG. 28 the nominal sweep line 143-144 is shownas a dashed line for reference purposes. The Y-coordinate displacementof the intercept between sweep line ends 144 and 156 at the right isshown as -ΔY and at the left between 143 and 155 as +ΔY. It may beunderstood that the Y-coordinate displacement at either end of theskewed sweep line 155-156 may be anywhere between -ΔY and + ΔY dependingon the direction and degree of rotation applied to the opposite ends ofthe flexible prism 33. It may be further understood that there may beother similar Y-coordinate displacement functions that may result fromthe individual and/or combined functions described relative to FIGS. 23to 28. Thus the axial twisting of the flexible prism 33 may assist inthe alignment and/or registration of the sweeping laser spot to theskewed horizontal outline lines of FIGS. 14, 15, 16 previouslydescribed.

The flexible prism 33 including various associated structural componentsand actuators may be in a nominal position as shown in FIGS. 29, 29A. Asshown, the long axis 145, 146 of the prism 33 is in the plane 23, 24 and26 of the sweeping laser beam 25 as shown in FIGS. 3, 23 and 29. A leftframe member 157 and a right frame member 158 support componentsassociated with the left and right ends of the prism 33. Tie rods 159may hold the frame members 157, 158 together for initial sub-assemblypurposes. Actuation components as hereinafter described are symmetricalleft and right as associated with frame members 157, 158. The prism 33is mounted for rotation between the frame members by small ball bearings160 which may be located within the ends of the prism 33.

In order to effect rotation of the prism 33, band clamps 161 areconnected to the ends of the prism 33 by clamp screws 162 and pivotblocks 163. As shown, left actuator means 164, 165 and right actuatormeans 166, 167 each have one end fastened to adjustment springs 164A andthe other end fastened to pivot blocks 165A. The bottom ends of theadjustment springs 164A are fastened to the frame members 157 and 158respectively by fasteners 166A. The top ends of the adjustment springs164A contact adjustable set screws 167A in the frame member 157, 158 foradjustment and/or alignment purposes. By using an assembly fixture (notshown) to support the prism 33, knife edge pivot blades 168 may beinterposed between the pivot blocks 163 and the pivot blocks 165 toprovide actuation linkage. Shaft support members 169 may then beassembled to the frame members 157, 158 using screws 170, and stub shaftscrews 171 may be run through the support members and into the shaftdiameters holes of the ball bearings 60. After removal of the assemblyfixture (not shown) the above described actuators and structuralelements may be employed to provide independent rotations to the leftand/or right ends of the flexible prism 33. The actuators 164, 165, 166,167 are preferably be of an equal displacement push-pull type: forexample in FIG. 29A, when activated by a right command the actuator 166pushes its associated pivot blocks 165, 163 and blade 168 to the rightand the opposite actuator 167 pulls (retracts) by an equal displacementto the right thereby allowing its associated pivot blocks 165, 163 andblade 168 to move to the right. When activated by a left command asimilar actuation occurs except that the displacements is to the left.Meanwhile, opposite springs 164 maintain the above described actuationsystem in compression by applying thrust forces from opposite sides ofthe right frame member 158. Thus the pivot blocks 163 may be actuated tomove right or left thereby providing clockwise or counter clockwiserotation about the ball bearing 160 for the clamp 161 and the right endof the flexible prism 33. Similar actuation components within the leftframe member 157 (FIG. 19) provide similar rotations for the left end ofthe flexible prism 33. In summary, it may be understood that withduplicate actuation systems at each end of the flexible prism 33, eachend of the prism may be rotated independently of the opposite end, thusthe angle of rotation and the X-coordinate deflection of the sweepinglaser beam 25 may be proportional and responsive to proportionalactuation commands.

The structure shown in FIGS. 29, 29A may also be used to support othercomponents of the inspection tool. As shown, the partially reflectingmirror 27 (FIGS. 1, 2, 3), that reflects a portion of the scanning laserbeam 25 to the grating 28, may be supported by brackets 172 secured tothe left and right frame members 157, 158. The partially reflectingmirror 27 may be retained by spring clips 173 to provide easy removalfor cleaning purposes. The underside of the left frame member 157supports the reflecting mirror prism 38 and the light detector orphotocell 40 (FIG. 3) that provide a margin delineation as at 23 and 24for the sweeping laser beam 25. The mirror prism 38 and the photocell 40may be retained together in a holder 174 that may be positionallyadjustable left and right and secured to the frame meber 157. Theundersides of the left and right frame members 157, 158 may support theleft and right ends of the transparent light conductor rod 35 andphotocells 36 (FIG. 1) located at each end of the rod whereby diffusedreflected light indicated by the arrow 175 from the sweeping laser beam25 may be captured by the rod as the beam sweeps across the workpiece 1and the captured light converted into electrical signals by thephotocells. The portions of the rod 35 adjacent the ends may be formedto an exponential curve 176 of progressively decreasing diameters toreflect captured laser light to the photocell 36. Sleeves 177 at eachend of the end 35 are provided to hold the photocells 36 adjacent theends of the rod 33. Spring wire clips 178 that snap over the sleeves 177are attached to the frame members 157, 158 and provide easy removal forcleaning of the rod 35, the sleeves 177 and the photocells 36.

In order to compensate for misalignment, for example, skew in theworkpiece, and as explained more fully hereinafter, the first few sweepsof the laser beam determine the position of the registration marksrelative to the beam sweep, the response being detected by the photocell36. If misaligned, then by either manual readout by the machineoperator, or computer calculation in conventional comparison circuits,the actuators 164, 165 and/or 166, 167 may be energized to effect twistof the prism or angular rotation thereof to effect registration of thesweep with the alignment marks.

THE DRIVE SCHEME

In order to register the sweep of the beam 25 with the movement of aworkpiece it is necessary to provide means to synchronize the beam sweepwith workpiece movement. To this end a gear drive train, such as isshown in FIG. 30, may be driven by the first motor 19 (FIG. 1) to effectrotation of the cylinder 9 and to provide an adjustable rotational driveratio between a high speed motor rotation and a low speed cylinderrotation. The adjustable drive ratio may be provided by adjusting thespeed and/or direction of rotation of a second motor 179 and anassociated differential gear system 180. Thus a small rotational speedadjustments may be added to or subtracted from the rotational speed anda surface velocity of the cylinder 9 relative to a fixed rotationalspeed provided by the fixed gear drive train ratio. For illustrativepurposes in FIG. 30 the directions of shaft rotations may be indicatedby curved arrows and the speeds of shaft rotations in revolutions persecond (rps) may appear below their description numbers. Likewise thenumbers of teeth in the gears and/or the threads in the worm screws mayappear below their description numbers. However it may be understoodthat there may be many other combinations of motor speeds, shaft speeds,and numbers of motor speeds, shaft speeds, and numbers of gear teeththat may be used to provide equivalent and/or different overall gearingratios for the gear drive train. The motor shaft 18 that rotates themultifacet mirror 17 may extend through the first motor 19 as smallershaft 181. A vibration isolation coupling 182 connects the motor shaft18 to a worm shaft 183 and a single thread worm 184. The worm 184effects rotation of a worm gear 185, horizontal shaft 186, and a firstmiter gear 187 of a pair of 1:1 ratio miter gears. The second miter gear188 is connected to shaft 189 and an upper miter gear within thedifferential gear system 180. In accordance with well known operatingprinciples of differential gear systems (such as in an automobiledifferential gear system), the rotation of the upper miter gear in onedirection causes rotation of a lower miter gear (not shown) in anopposite and/or reverse direction through rotation of an intermediatemiter gear (not shown). The intermediate miter gear rotates on a shaftsecured to the housing 191 of the differential gear system 180, whilethe lower miter gear rotating in the opposite direction, is coupled toand effects rotation of a lower shaft 192. The lower vertical shaft thusrotates a second pair of 1:1 ratio miter gears 193, 194, a horizontalshaft 195, and a gear 196. The gear 196 rotates another gear 197, wormshaft 198 and a single thread worm 199. The worm 199 effects rotation ofa worm gear 200, cylinder shaft 201, and the cylinder 9.

The above described gear drive train may be employed to provide a fixeddrive ratio and rotational speed of the cylinder 9 assuming that thesecond motor 179 and the differential housing 191 are not rotating.However, if small plus or minus variations from the fixed drive ratioare required by the inspection tool, and/or by the computer, and/or bythe operator such variations may be applied to the gear drive train byenergization of the second motor 179. The motor 179 then effectsrotation of a worm shaft 202 and a single threaded worm 203. The worm203 rotates a worm gear 204 attached to the differential gear systemhousing so that if the differential gear system housing so that if thedifferential housing 191 is rotated at, for example, 1 revolution persecond in a given direction the rotational rate of the lower verticalshaft 192 may be varied by 2 revolutions per second in the same givendirection. This varied speed may additive to or substractive from thefixed rotational speed of the shaft 192 depending on the direction ofrotation of the second motor 179.

The variable speed motor 179 may preferably be of a two phase steppingmotor type whereby its rotational direction and speed may be readilycontrolled by a fixed and/or variable stepping periodicity of anassociated tow phase power supply (not shown).

The variable speed second motor 179 may be employed to make largerY-coordinate dimensional adjustments on the workpiece 1 relative to thesweeping laser beam spot than the smaller adjustments that may bereadily accomplished by the flexible prism 33. (FIGS. 29, 29A). Suchlarger and smaller adjustments in the Y-coordinate may be similar ineffect to the larger and smaller X-coordinate adjustments provided byrotating the grating 28 (FIGS. 21, 22). An extension of the previouslyused X-coordinate example into the Y-coordinate may be useful indescribing the utility of such larger adjustments. As previouslydescribed, the circuit pattern design of a workpiece 1 may be made tosintered dimensions where as the workpiece may be inspected to largerunsintered dimensions, i.e., dimensions prior to sintering shrinkage.Thus the design data may show a 5 inch square circuit pattern and theinspection tool may inspect the Y-coordinate unsintered dimensions as5.000/0.828 = 6.0386 inches. The sintering factor 0.828 or other factorsmay be used to account for the sintering shrinkage and may be applied tosintered X and/or Y-coordinate circuit pattern dimension within patternoutline 50 to thereby obtain unsintered inspection dimensions. Thus withan effective diameter of 0.001 inch for the sweeping laser spot, 1000sweep lines per inch may be used in the Y-coordinate. Correspondinglythe 6.0386 unsintered dimensions of the workpiece may require 6039 sweeplines to be applied by the inspection tool. However since 6039 as anumber is so close to the number 6000 it may be more convenient and savecomputer time to use 6000 scan lines to inspect the workpiece 1. Theconvenience may be that the design data for the sintered workpiece 1 isbased (in the example) on a 0.005 inch X-Y matrix grid system includinga 0.005 inch sub-grid. In using the grid system it may be convenient fora circuit designer to locate via hole centers at matrix 0.005 inch gridintersections and the centers of 0.005 inch wide conductor lines on gridlines (see FIGS. 7B, 8B). The edges of a 0.005 inch wide circuit linemay be located 0.0025 inches either side of a grid line and therebycoincide with a sub-grid line. Then when the design data (sintereddimensions) is expanded for inspection purposes (unsintered dimensions)the design data may be multiplied by a factor of 1.2l × 10³ whereby a5.000 inch Y-coordinate dimension, 5.000 × 1.2 × 10³ = 6000 sweep lines.Similarly for the 0.005 inch matrix grid and circuit conductor lines,0.005 × 1.2 × 10³ = 6 sweep lines. Thus this procedure produces aninspection matrix grid based on an even 6 sweep lines with the centersof via holes and conductor lines coinciding with the matrix grid (seeFIGS. 7A, 8A). Likewise the edges of circuit conductor lines may now be0.0025 × 1.2 × 10³ = 3 sweep lines from the matrix grid lines. However,since the Y-coordinate unsintered dimension to be inspected may be6.0386 inches, means may be provided to spread 6000 scan lines over6.0386 inches. Such means may be provided by the variable speed motor179 (FIG. 30) and the differential gear system 180 whereby therotational speed of the cylinder 9, as driven by the fixed gear ratiocomponents of the gear train, may be increased slightly to spread 6000sweep lines over 6.0386 inches. Since a fixed gear ratio may be designedfor 6000 scan lines over a 6.000 inch Y-coordinate dimension theincrease in rotational speed of the cylinder 9, in the example given,would be in the ratio of 6.0386/6.000 = 1.0064333 or about a 0.6433%speed increase.

Various approaches may be used in the design of the drive gear trainFIG. 30 and/or its equivalent. Assuming initially (subject to latercorrection) that the workpiece(1) (FIGS. 4, 5, 6) to be inspected withinthe outline 50 may have dimensions of 6.000 inches by 6.000 inches, theoutline 50 is centered in a 7.000 by 7.000 inch area of workpiecematerial to provide 0.500 inch margins outside of the outline 50.Assuming a drive motor 19 (FIG. 30) rotation of 100 revolutions per sec(rps) while driving the 18 facet mirror 17 and the single thread worm184, the laser beam 25 sweep in lines per second may be calculated,i.e., 100 × 18 = 1800 lines per second. The circumference of thecylinder 9, allowing for 1/2 the thickness of the workpiece, may beequal to the length of 4 pieces of worksheet material, i.e., 4 × 7.000 =28.000 inches. The rotational speed of the cylinder 9 may then becalculated, 1800/28,000 = 0.0642871 revolutions per second (rps). Thiscorresponds to 15.5555 seconds for one revolution of the cylinder 9 withfour workpieces or slightly under four seconds to inspect one workpiece.With the motor 19 and the worm 184 rotating at 100 rps, the driving gearratio is then calculated for the cylinder, 100/0.0642871 = 1.555.55 gearratio. With this ratio in mind, the single thread worm rotates the 20tooth worm gear 185, and shafts 186, 189, 192 and 195 at 100/20 = 5 rps.The 18 tooth gear 196 rotates the 14 tooth gear 197 and the worm shaft198 at 5 × 18/14 = 6.428571 rps. The single thread worm 199 rotates the100 tooth worm gear 200, the cylinder shaft 201 and the cylinder 9 at,6.428571/100 = 0.06428571 rps as previously calculated to be the assumedspeed. However, the assumed cylinder speed may now be corrected tospread 6000 sweep lines over 6.0386 inches by using the previouslycalculated speed increase ratio 1.006433 which may be applied to thedrive gear train through the functioning of the differential gear system180.

With the upper vertical shaft 189 continuing to rotate at 5 rps. thespeed of lower vertical shaft 192 may be increased from 5 rps. to 5 ×1.006433 = 5.032165 rps. by rotating the differential housing 191 at 1/2of the differential speeds between the shafts 189, 192. Thus therotational speed of the housing 191 may be determined, 5.032165 - 5. =0.032165 rps, and divided by 2 = 0.0160825 rps. As described, thehousing 191 is rotated by a 50 tooth worm gear 204 and a single threadworm 203 having a gear ratio of 50 whereby the speed of the worm shaft202 and the second motor 179 0.0160825 × 50 = 0.804125 rps.

The second motor 179 and its two phase power supply may be commerciallyavailable types providing 180 step positions per one rotation of themotor driven worm shaft 202. A stepping motor of this type rotates itsrotor and shaft through an angle of 360°/180° = 2° per step. As anexample of the type of stepping motor, it may have two types ofelectrically isolated pole windings, each on separate poles: a firstphase winding and a second phase winding. The power supply, in thatcase, is arranged to provide suitably phased voltages to the first andsecond phase windings whereby the motor shaft rotated one step at atime.

One of the characteristics of a stepping motor is that the rotor of themotor may remain in a fixed positional alignment with a pole (or groupsof similarly magnetized poles) for as long as a suitably polarized andphased first or second phase voltage is applied to the polar coilwindings of the motor. Then for example, if a first phase voltage thatis holding the rotor in a fixed rotational alignment is shut off and 8suitably polarized second phase voltage is turned on, the rotor may makeone rotational step of 2° and remain there until the second phasevoltage is shut off. Then by turning on a reverse polarized first phasevoltage another 2° step may be taken in the same rotational direction,etc. Thus the rotor may stepped through 2° and stopped 180 times in forone 360° rotation of the worm shaft 202. The time interval between the2° steps is controlled by suitable timing and phasing of the two phasepower supply whereby the rotational speed of the motor's rotor and theworm shaft 202 are controlled. The power supply may include well knownmeans to convert 117 to volt 60 cycle single phase commercial power intosuitably phased lower voltage power for the stepping motor 179. A shorttiming signal pulse from an external signal source may provide thetiming control for the power supply whereby the motor's rotor then takessingle 2° steps. For example, a positive signal pulse may provide a 2°clockwise step or a negative signal pulse may provide a 2° counterclockwise step.

Various means may be used for generating timing signal pulses to controlthe rotational speed of the stepping motor 179 and the worm shaft 202.Preferably the pulse generating means is flexible so that the timingbetween pulses may be varied to control the speed of the stepping motorand thereby to provide for various anticipated sintering shrinkages ofthe workpiece 1. At the previously calculated speed of 0.804125 rps. forthe stepping motor 179, the motor requires 0.804125 × 180 = 144.7425steps per second at 2° per step. A high frequency clock or itsequivalent provides high frequency pulses which may be applied to a highfrequency pulse counter. The pulse counter may count the high frequencypulses and at repeating and predetermined pulse counts issue lowerfrequency pulses to control the two phase power supply and the steppingmotor 175. The photocell 40 (FIGS. 3, 29) may be used to generate asingle high frequency pulse from each sweep of the sweeping laser beam25, and thus may be considered the equivalent of a high frequency clock.Since in the example given there were 1800 laser beam sweeps per secondthe photocell 40 generates 1800 pulses per second. If the stepping motorrequires 44.7425 stepping pulses per second, as previously calculated,the predetermined pulse count number may thus be calculated,1800/44.7425 = 40.230206 high frequency counts per stepping motor pulse.Since this high frequency count number is not an integer number two ormore counters may be required to approximately simulate the number: letthe first counter count up to a next higher integer number such as 41,thus 1800/41 = 43.9024 and subtracting, 44.7425 - 43.9024 = 0.8401.Next, 1800/18401 = 2,142 and use a next higher integer 2143 for thesecond counter to issue respective supplemental stepping motor pulses.Then the stepping motor pulse rates from the first and second countersmay be added:

1st: 1800/41 = 43.9024 stepping motor pulses per sec

2nd: 1800/2143 = 0.8399 stepping motor pulses per sec

1st + 2nd counters = 44.7423 stepping motor pulses per sec

This number may approximately simulate the required number of 44.7425stepping pulses per second for practical purposes when the flexibleprism 33 of FIGS. 23-29 deflects the sweep line 143, 144 of the laserbeam to provide a dimensional equivalent for the difference between thetwo pulse rate numbers. It may be noted that by continuously providingelectrical power to the counters, the stepping motor power supply, andthe laser beam the stepping motor 175 remains in a functional type of"step synchronism" with the mirror drive motor 19 during periods whenthe motor 19 may be decelerated to a stop, during a stop, andaccelerated from a stop to a constant and/or variable running speed.Thus the "step synchronism" speed ratio between the mirror drive motor19 and the stepping motor 175 remains fixed by the high frequencycounting numbers previously set into the counters. The "stepsynchronism" speed ratio may also be changed by having the inspectiontool operator and/or the computer set suitable new numbers into thecounters whereby other Y-coordinate shrinkage ratios of the workpiece(s)1 may similarly accomodated.

In summary, the gear drive train in combination with the flexible prismmay be employed to make high precision adjustments for variousY-coordinate shrinkage and/or expansion ratios of the workpiece. Thiscombination provides for average gross sintering shrinkage ratioadjustments by the variable ratio gear drive train and average verniersintering ratio adjustments by partial rotation of the flexible prism,while concurrently the flexible prism may also make small shrinkage orexpansion adjustments for individual workpieces to accomodate ratiosand/or factors other than sintering shrinkage ratios.

THE SWEEPING LASER SPOT AND Y-COORDINATE REGISTRATION

Many of the Y-coordinate functions of the sweeping laser spot may beunderstood from FIG. 31 and associated descriptions. The focused laserbeam spot 205 may be sweeping from left to right across the surface of aworkpiece 1. The laser light energy is distributed across anX-coordinate diameter 207, 208 or a Y-coordinate diameter 209, 210 ofthe sweeping spot 205, approximately as projected below in a bell shapedcurve 211. The laser energy of the curve 211 is greatest in the broadlyrounded central top and decreasing in relatively steep sides slopingdownward from the top to a much lower energy at the rim of the bellcurve. The laser energy is focused in a manner such that about 80% ofthe laser energy of the spot is within a circular area having anX-diameter 212, 213 or a Y-diameter 214, 215 of 0.001 inches. The largercircular area that includes the 0.001 inch diameter area may includeabout 90% of the laser energy and may have a diameter of about0.00135inches. Thus considering that the larger laser spot circle of diameter207, 208 includes approximately 90% of the laser spot energy and isconcentric with the smaller circle of diameter 212, 213 having 80% ofthe laser spot energy, subtracting the area of the smaller circle fromthe area of the larger circle, the differences between the areas isnearly equal to the area of the smaller circle but only contains about10% of the laser spot energy. A still lower level of laser spot energymay extend over a much larger area having a diameter 216, 217 on thebell curve 211 with a residual 9% of laser spot energy outside thediameter 207, 208 spread over such a large area that the residual lowlevel energy may be disregarded for practical measurement and inspectionpurposes. As projected to the right of the circular laser spot 205,photocell voltage response curve 218 shows the response of thephotocells 36 (FIGS. 1, 29) to various levels of laser light from thesweeping laser spot 205 such as may be reflected from the workpiece 1and conducted to the photocells by the transparent light conductor rod35. The voltage response of the photocells 36 is at a maximum when thelaser spot 205 of diameter 209, 210 sweeps entirely over a white area ofthe workpiece 1 and at a minimum when the laser spot sweeps entirelyover a dark area such as registration lines 77A, 77B, 77C (FIG. 17) orthe conductor patterns (FIGS. 7A, 8A).

To illustrate the voltage response curve 218 consider that the laserspot is projected to the right to the response curve by the horizontaldash lines as shown. The dash lines divide the larger diameter 210, 209into 8 equal lengths and correspondingly as cords divide the laser spotcircle into sectors having various areas. Starting at the bottom andtangent to the point 210 a horizontal top edge 206 of a dark horizontalregistration line 78 (FIG. 17) may be thought of as moving upwardsacross the circle until it becomes a top tangent at the point 209. Whenthe dark top edge 206 is at the bottom tangent point 210 the laser spotcircle may be entirely on a white area of workpiece material and thevoltage from the photocells 36, as projected to the right on theresponse curve 218, is at a maximum. When the dark top edge 206 is atthe top tangent point 209 the laser spot circle is entirely on a darkregistration line 78 with near zero photocell response. At variouslocations between the bottom tangent 210 and the top tangent 209 the topedge 206 of the registration line is a horizontal cord of the largerlaser spot circle dividing the circle into a dark lower sector and awhite upper sector with the photocell's 36 responding to a decreasinglywhite sector area as shown by the curve 218. There may be relativelylittle laser spot energy in the lower sector between the tangent point210 and a cord 219 tangent to the inner circle or in an upper sectorbetween a tangent cord line 220 and the tangent point 209. The lowsector energy occurs from the small areas of the sectors and the lowlevel of laser energy occurring between the outer circle of diameter207, 208 and the inner circle of 212, 213 diameter. Thus these smallsectors show as approximately vertical lines 210, 219 and 220, 209 onthe response curve 218 as the dark area of the registration line movesfrom point 210 to point 209 and progressively obscures the white areawithin the outer circle. The curve 218 is slightly S-shaped between thepoints 219 and 220 and essentially symmetrical about a projected centraldiameter cord 207, 208 of the outer circle. A straight line drawn fromthe point 219 to the point 220 closely approximates the curve 218between these points and provides a linear voltage reference levelbetween the points. Since within the outer circle the cords 219, 220 mayalso be tangent to the inner 0.001 inch diameter circle the linearvoltage reference level may be used to closely approximate the interceptposition of the horizontal dark edge 206 with the vertical diameter ofthe inner laser spot circle. As shown in FIG. 32 the top dark edge 206of the horizontal registration line 78 may be about 1/2 way up thevertical 0.001 inch diameter and when projected to the right tointercept the straight line 219, 220 approximation of the response curve218 the photocell voltage V may be approximately 1/2 of the maximumphotocell voltage V max. Thus it may be understood that the photocellvoltage response voltage V may be at levels proportional to various cordintercepts of the top dark edge 206 as the 0.001 inch diameter laserspot sweeps across a horizontal registration line 78. The horizontalregistration line 78A may be 0.030 inches wide for a stable voltagemeasurement during the laser sweep. The proportional voltage V may beamplified, measured and clamped at the measured voltage level for aperiod of time. The clamped voltage V may be suitably polarized andapplied to the actuators 164, 165, 166, 167 (FIG. 24) of the flexibleprism 33 to deflect the sweep line 143, 144 (FIG. 23) of the sweepinglaser beam 25.

The enlarged area of the registration pattern 76 (FIG. 13) may otherwisebe shown as small areas 49 (FIGS. 4, 5, 6) and duplicated in the leftand right margins of the workpiece 1.

The clamped voltage V developed from left margin horizontal registrationlines 78 may be applied to the left actuators 164, 165 (FIG. 29) andfrom the right margin horizontal registration lines 78 the rightactuators 166, 167.

The inspection tool may include a computer (not shown) operating fromthe measured voltage V whose directives command signals determine asuitable voltage and polarity to be applied to the left 164, 165 and/orright 166, 167 actuators of the flexible prism 33. By such commandsignals the actuators provide + or - rotation to either and/or both endsof the flexible prism 33 whereby either a bottom tangent line 219 (FIG.31) or a top tangent line 220 of the 0.001 inch sweeping laser spot maybe deflected into approximate coincidence and/or registration with thetop dark edge 206 of the horizontal registration lines 78A located inthe left and/or right margins. If a skewed conditions occurs in thecircuit pattern outline 50 (FIG. 16) between the left and right patterns49 (FIGS. 4, 5, 6) two successive laser spot sweeps across the workpiece1 may be required to pick up registration signals from the top darkedges 206 the widely separated registration patterns 49 located in theleft and right margins; i.e., in this instance the left registrationpattern would be lower than the right registration pattern and thus theleft pattern might be missed by a laser sweep that picks up a portion ofthe right pattern. However the next successive laser sweep might pick upa portion of the left registration pattern and the computer may thenprovide a suitable voltage and polarity for the left and the rightactuators of the flexible prism 33 to provide a skewed laser scan line155, 156 (FIG. 28) for registration purposes. Other horizontalregistration lines 78B, 78C of the registration patterns 76 maysimilarly be used to progressively improve registration. Likewise otherregistration patterns 49 in the left and right margins and periodicallylocated from top to bottom of the workpiece 1 may periodically correctregistration as the workpiece is moved under the sweeping laser beam.

The computer may also be used to provide "rejection signals" when thedark edge 206 is greater than ±0.001 inch from its nominal Y-coordinateposition relative to the sprocket holes 3 (FIG. 1) or the registrationholes 53, 54, (FIGS. 4, 5); and may also reject a workpiece when theY-coordinate dimensions of the dark edges 206 in the left and rightmargins are separated by more than 0.002 inches due to a skewedcondition. The above limits on Y-coordinate registration dimensions(FIGS. 10 to 16) may be similar to dimensions previously describedrelative to limitations on circuit line and via hole locations (FIGS.7A, 8A) previously described relative to FIG. 9 since the registrationpattern and the circuit pattern may be based on using the same 0.006inch matrix grid and 0.001 inch sub-grid system. Thus if the bottom ortop tangents 219, 220 (FIG. 31) of the sweeping laser spot circle arebrought into approximate Y-coordinate registration with the top darkedge 206 of a registration pattern, the tangents may thereafter be inapproximate registration with the horizontal top or bottom line edges ofthe conductor pattern circuit lines and the centers of via holes.

In summary, the Y-coordinate registration represents a major and uniquefeature of the inspection tool inasmuch as without registration thesweeping laser spot circle could encounter a horizontal line edgeanywhere within the diameter of the circle and individual calculationsbased on the photocell response voltage V for 36,000,000 or more zonesof 0.001 inch diameter in a 6 inch square workpiece may be required todetermine the locations of top and bottom circuit line edges forinspection purposes. These individual zone calculations of course wouldreduce the inspection accuracy of the inspection tool since the voltageV would not have time to stabilize for each 0.001 inch circular spotzone. Additionally, individual zone calculations might considerablyincrease inspection time since such individual calculations wouldincrease the work load of the computer.

THE SWEEPING LASER SPOT AND X-COORDINATE REGISTRATION

Many of the X-coordinate functions of the sweeping laser spot may beunderstood from FIG. 32 and associated descriptions. The X-coordinatefunctions are similar in part to the Y-coordinate functions. In sweepingfrom left to right across the workpiece 1 the focused laser spot mayencounter vertical portions of vertical registration lines 77A, 77B, 77C(FIG. 17) and/or vertical portions of vertical conductor pattern lines(FIG. 7A, 7B) while concurrently a synchronous portion of the samefocused laser spot may be intercepted by the partially reflecting mirror27 (FIG. 1) and reflected as a focused spot on the grating 28. In FIG.32 these progressive positions 221, 222, 223 of the 0.001 inch diametercircular portion sweeping laser spot may be shown as the spot approaches221, intercepts 222, and enters a dark area 223 having a vertical leftedge 224 on the workpiece 1. A corresponding voltage response curve 225of the photocell 36 (FIG. 1) with the centers of the circles 221, 222projected downward to the curve may show the voltage response as thelaser spot sweeps from left to right across the vertical left edge 224.With the laser spot circle 221 entirely on a white area the voltageresponse may be maximum (V_(max)) and when the circle 223 is entirelyover a dark area the voltge may be a minimum. The steepest part of thecurve 225 occurs as the vertical diameter and the center of the circle222 sweep over the vertical dark edge 224. By differentiating andrectifying the photocell voltage response, a sharply peaked pulse curve225 is developed that is symetrical and centered on the dark edge 224.When sweeping from a dark area to a light area the laser spot induces aphotocell response curve (not shown) that is the reverse image of thecurve 225 and result in another pulse curve similar to the curve 225 andlikewise centered on a vertical dark trailing edge. Meanwhile thesynchronous laser spot sweeping across the grating 28 (FIGS. 1, 2, 8A to8D, 21) may develop similar pulses 89 (FIGS. 18D, 31) except that thepulses 89 may be regularly repetitive and centered 0.001 inch apart aspreviously described. In this connection the computer may measure the +or - time difference at between the center lines of the response curvepulse 225 and the nearest grating pulse 89. The time difference may thenbe converted, in a conventional manner to a higher voltage of thecorrect polarity with the voltage being proportional to the timedifference, and the voltage level clamped at that level and then appliedto suitable actuator components 115, 117 or 116, 118 (FIG. 21).

As previously described, the registration patterns 76 (FIG. 17) or 49(FIGS. 4, 5, 6) may be located in the left and right margins of theworkpiece 1. When the response curve pulse 225 are derived from aregistration pattern 49 in the left margin of the workpiece 1 the timedifference voltage is applied to the actuator components 115, 117 (FIG.21) to physically move the Grating 28 up to ±0.001 inch to the left orright whereby the grating pulses 89 (FIG. 32) may be moved left or rightinto alignment and/or registration with the voltage response pulse 225.When the response curve pulse 225 may be derived from a registrationpattern 49 in the right margin the time difference voltage are appliedto the actuators 116, 118 to physically rotate the grating 28 therebycontracting or expanding the effective length of the grating pulse trainto bring the grating pulse 89 into alignment and/or registration withthe photocell response pulse 229. It should be understood that there maybe dimensional restraints on such physical displacements and rotationsof the grating 28 which may not correspondingly exceed the restraints onvia hole alignment (FIG. 9) as previously described. In summary, afteralignment and/or registration of the grating pulses with theregistration pattern pulses the grating pulses should also be inregistration with the X-coordinates of the inspection matrix grids andthe circuit line patterns.

ALIGNMENT AND CALIBRATION

The inspection tool may preferably be carefully aligned and calibratedto provide inspection accuracy for dimensions smaller than 0.001 inch.Relative to the workpiece the X-coordinate vector across the workpiecemay be at a 90% angle to the Y-coordinate vector along the length of theworkpiece, the latter being parallel to the direction of motion of theworkpiece during inspection. The sweep line vector of the focused laserspot across the workpiece preferably may be at a slight "lead angle" of0.001/6.000 from the X-coordinate vector to account for the motion ofthe workpiece as the laser spot sweeps from left to right across theworkpiece. Micrometer calibration means (not shown) may be used tohorizontally shift the axis of the rotating mirror 17 (FIG. 30), theshaft 18, the mirror drive motor 19, and the shaft 181 about theflexible coupling 182 as a pivot point to achieve a suitable lead angle.

A manually pre-calibrated nominal workpiece may be slowly fed into theinspection tool by turning off and holding the mirror drive motor whileslowing pulsing the stepping motor to provide a slow speed drive. Thenby manually rotating the mirror the laser spot is set to theprecalibrated positions on the workpiece and the grating adjusted toregister with these positions by using the adjustable set screwspreviously described. The precalibration may be assisted by microscopesand voltmeters, and a more accurate calibration may then preferably beaccomplished with the mirror drive motor turned on and with theinspection tool running under full dynamic running conditions. Underdynamic conditions adjustments of various other components may berequired until the inspection tool reports a zero error condition for anominal workpiece that has been previously inspected and accepted forcalibration purposes.

In order to equalize the displacement provided by the actuators of thegrating and the flexible prism, conventional potentiometers may beemployed. By using suitable reference voltage signals, for example, froma computer, the voltage levels of such reference signals may be clampedat fixed voltage levels until changed by subsequent reference signals.Of course included in the computer program is such a restraint that theclamped voltage levels may only be changed during a "fly-back" period;i.e., after the left-to-right sweeping laser spot has passed beyond theright margin of the workpiece and before it enters the left margin. A"fly-back" period (or more technically correct, a "fly-forward" periodin this instance) may occur as the laser beam from the laser source isintercepted by the line between two adjacent faces of the multifacetrotating mirror with each of the two faces then reflecting separatelysweeping laser beams which could confuse the photocell response. Sincethe "fly-back" time represents a small loss of laser beam sweep time therotational speed of the workpiece supporting cylinder is slowedproportionately to avoid gaps between sequential laser sweep lines.

In passing, it should be noted that the inspection tool may be employedwith a tape, punch card, or computer, it being recognized that what isbeing accomplished is the inspection of a workpiece and morespecifically the pattern thereon to determine whether the pattern on theworkpiece matches a predetermined perfect pattern. Thus whether a bellor whistle is employed to indicate a lack of match or a pattern defector a more sophisticated detection scheme is use such as a computer tostore in a digitized format the information relative to the pattern andits comparison is immaterial to the present invention. Obviously, in aninspection scheme where a comparison must be made for a single partnumber or a small number of part numbers, a punch card or tapecomparison scheme may be employed. Alternatively, if a large number ofdifferent patterns are to be inspected, a tape or computer scheme usingbulk storage such as disc or tape is to be preferred. Additionally, itshould be recognized that the scheme employed could be used with a pairof inspection stations with a simple comparator, the first stationinspecting the workpiece and the second station inspecting the masterpattern, the output, for example of the photocells being compared in thecomparator such that if a fault exists, an error signal is displayed.However, it should be noted that in the preferred embodiment, a computersuch as the IBM 360/Mod. 65 is the preferred data and comparison source.

CONTROL AND COMPARISON

Various methods may be used to interface the inspection tool's laserscan system and its computer system. A variety of computer systems withmemory banks are commercially available. Many commercial computers maybe programmed to compute using new and/or stored data in equivalentand/or interchangeable forms such as analog, decimal, binary, voltage,time, etc. and/or combinations thereof. The computer programming forsuch computers is well known to one skiled in the art and thus is asubject that need not be described herein except for a few schematicblock diagrams.

The laser scan system generates "workpiece inspection data" in "realtime" as the workpiece 1 progresses through the inspection tool. The"workpiece inspection data" may be compared for agreement withcalculated and/or previously stored "correct data images" provided bythe inspection tool's computer. Various types of computer programs maybe used when such workpiece data is compared for agreement with thecorrect data image depending on the size and addressing speed of thecomputer and its memory bank.

Various types of computer programs may be employed with inspection toolcomponents such as are included in schematic block diagram FIG. 34. Somecomputer programs may use more or less components and/or the componentsmay be interconnected differently than shown in FIG. 34. The componentsare shown spread apart for block diagram purposes but may be located inand/or on the inspection too chassis while the computer components maybe located in separate cabinets or in the main computer cabinet. Theinterconnecting cables shown may include one or more electricalconductors as may be required to perform their functions.

The laser scan system and associated amplifiers, counters and addressersare used in several functions and are described first to avoidrepetition in the descriptions of such functions. Referring now to FIG.34, the first or grating photocell 32 is connected by a cable 241 to anX-coordinate signal amplifier cabinet 242 where the photocell signal islinearly amplified, differentiated, and full wave rectified to providethe X-coordinate incremental marker pulses 89 (see FIG. 18D and 18G).The cabinet 241 includes a pulse counter for the marker pulses 89 withthe pulse counting being initiated at a position corresponding to thewide laser energy transmitting line 89 (FIG. 18E) of the grating 28 andthe slope 88 (FIG. 18F) of the grating photocell response curve. Thepulse counting initiating location may be somewhat to the left of theregistration patterns 45 (FIGS. 4, 5, 6) in the left margin of theworkpiece 1 so that the registration patterns are included in an X and Ycoordinate recognition program as described later. The X-coordinatepulse count may be used "as is"and/or converted to an X-coordinateaddress for the momentary location of the sweeping laser spot and thentransmitted to the gate section 243 of the correct data memory bank 244by the cable 246. The cable 246 also transmits the linearly amplifiedvoltage of the photocell 32. The third or margin marker photocell 40 isconnected by a cable 247 to a Y-coordinate amplifier cabinet 248 wherethe photocell signal is linearly amplified, differentiated, and halfwave rectified to provide a single Y-coordinate marker pulse from a leftmargin position to the left of the registration patterns for each singlesweep of the laser beam. The cabinet 248 includes a Y-coordinate markerpulse counter that provides data on the momentary Y-coordinate sweepline of the laser inspection spot. The Y-coordinate pulse count may beused "as is" and/or converted to a Y-coordinate address and transmittedby a cable 249 to gate section 243 of the memory bank 244. The cable 249also transmits the linearly amplified voltage of the photocell 40. Thesecond or workpiece photocell 36 is connected by a cable 251 to aworkpiece data amplified cabinet 252 where the photocell signal islinearly amplified, differentiated, and full wave rectified to provideedge marker pulses for the white to dark and/or dark to white edges ofvarious patterns present on the worksheet 1. The edge marker pulses andthe linearly amplified voltage of the photocell 36 are transmitted by acable 253 to a comparator cabinet 254.

The functions of the gate 243 of the correct data memory bank 244 mayinclude gating or switching data and/or signals from various componentsof the inspection system to other components with the controls for suchgating being provided by a computer program previously entered andstored in a main frame computer 256. Cables 257, 258 interconnect thememory bank 244 to the computer 256. The gating section 243 of thememory bank may be provided with a permanent data memory of thestandardized X and/or Y coordinate locations for registration patterns,part number patterns, other data patterns including X and Y sinterngshrinkage rates, circuit line outline patterns, etc. that may be commonto all workpieces being inspected. Thus for example, when provided withX and Y coordinate data by cables 246, 249 the gate section 243 may beprogrammed to segregate registration pattern signals from part numberpattern signals etc. or circuit pattern signals by appropriate gatingand/or switching programs. Such switching progams may then redirect thepattern data for internal use and/or redirect the pattern data and/orgating signals to other components of the inspection tool for usetherein and/or further data processing.

Functions and signal responses of various electro-optical,electro-mechanical, and computing components of the inspection tool havebeen described previously and need not necessarily be repeated relativeto FIG. 34 except to briefly describe data signal, command signal,computing, and computer programming interrelations.

A computer program is applied to the main frame computer 256 from aremote terminal or from a local magnetic disc file 261 by means of cable262, and the remote program may be stored in the disc file 261 by meansof cable 263. Basic circuit pattern design data may be applied to themain frame computer 256 from a remote terminal in a conventional manner,the design data applied may have been pre-expanded for inspection use toa correct data image(s) (0.006 inch X, Y grid with 0.001 inch sub-grid).For an unsintered circuit pattern(s) the data may be applied to thememory bank 244 by means of cable 258 and/or applied to the disc storagefile 261 by means of cable 263. Alternatively if the nominal design datafed to the computer by the terminal has not been expanded for inspectionuse (0.005 inch X, Y grid with 0.005 inch sub-grid) the computer may usesuch data to generate a correct data image 0.006 inch X, Y grid with0.001 inch sub-grid) for inspection purpose use, as describedheretofore, and the correct data image for the inspection of a circuitpattern then applied to the memory bank 244 and/or the disc storage file261. Of course the computer 256 may provide a production control dataand/or additional data to remote equipment in a well known manner.

The comparator 254 intercommunicates data with the main frame computer256 by means of cables 263, 264, with the gate section 243 by means ofcables 266, 267, and with the correct data image memory bank 244 bymeans of cables 268, 269. The cables 253 provides the comparator 254with amplified white and/or dark signal data from the workpiece 1 andmarking pulse data to the edges of white and/or dark patterns on theworkpiece. As the worksheet passes through the laser inspection or workzone the sprocket holes 6 (FIG. 1) of the workpiece engages the sprocketpins 12 of the cylinder 9 with sufficient accuracy such that programmedX-Y gating signals from the gate section 243 may be used to segregratevarious patterns on the worksheet such as registration patterns frompart numbers etc. and/or from circuit pattern areas.

The gatng program may be activated for each of four sequentialworkpieces being inspected, for example, by using four reflecting marks273 (FIG. 1) on the end of the cylinder 9 with the marks beingpositioned to correspond with the separating lines 44 between sequentialworkpieces. A light source 274, the reflecting mark 273 and a cylinderphotocell 276 cooperate to provide an activating signal to a cable 277connected to a signal amplifier in the comparator 254. The amplifiedactivating signal is passed to the gating section 243. It should berecognized that the gating program could also be activated by marks onthe workpiece.

As the sweeping laser spot traverses the leading edge margin 48 (FIG. 4)of the workpiece(s) 1 the activated gate section 243 segregates the partnumber data on cables 253, 266 from other data, decodes the data, anduses the decoded part number data to select and designate a correct dataimage from data in the data bank 244. Concurrently the gate section 243segregates X and Y sintering shrinkage rate data, decodes the data, andtransmits the decoded data to the main frame computer 256. The computer276 is programmed to encode the decoded X, Y sintering shrinkage data toformat signals suitable for controlling the grating motor 132 (FIG. 2)and the stepping motor 179 (FIG. 30). Such X and Y format signals aretransmitted by cables 278, 279 to power amplifiers and controllers 281,282 which provide cables 283, 284, 286 with suitable power controls forthe motors 132, 179. By such means the encoding disc 134 of the motor132 (FIG. 22) cooperate to rotate the grating 28 which may now provide"nominal" X-coordinate inspection dimensions that include sinteringshrinkage compensation. Similarly by such means the stepping motor 179adjusts the rotational speed of the cylinder 9 which provides "nominal"Y-coordinate inspection dimension that include sintering shrinkagecompensation.

Also concurrent with part numbers and sintering shrinkage data from theleading edge margin 48 (FIG. 4) of the workpiece 1, the activated gatesection 243, using data on cables 253, 266 segregates the data signalsof vertical registration lines 77 A, 77B, 77C (FIG. 17) from horizontalregistration lines 78A, 78B, 78C in both the left and right margins ofthe workpiece(s) 1. The segregated vertical and horizontal registrationline data is returned to the comparator 254 by means of the cable 267.In the comparator 254 line edge pulses from the vertical registrationlines in the left margin are compared for X-coordinate displacementrelative to the grating line edge pulses from cables 246, 267. Thecomparator 254 generates a signal that is proportional to the magnitudeand direction of the X-coordinate displacement, amplifies the voltageand power of the signal, and transmits the amplified signal to suitablegrating actuators 287 by means of a cable 288. Suitable gratingactuators 287 then provide vernier motion to move the grating 28 to theleft or right to bring the grating line edge pulses into alignment withline edge pulses of the vertical registration lines. This procedure maybe repeated for vertical registration lines periodically located lowerin the left margin of the workpiece and thereby periodically registeringthe grating to the left edge of the circuit pattern area. A similarprocedure may be used with the vertical registration lines in the rightmargin of the workpiece whereby suitable actuators 287 may apply avernier rotary action to the grating 28 to bring the grating pulses intoregistration with the right edge of the circuit pattern area.Additionally, in this instance, perodic grating measurements may betaken of a dimension between vertical registration lines in the leftmargin of the workpiece and corresponding lines in the right margin.This dimension should preferably be taken before vernier gratingadjustments are made. If the dimension differs from the "nominal"dimension including manufacturing tolerances the comparator 254 mayissue a power amplified reject signal on cable 289 to an accept orreject marker 70 that applies a reject mark in the right margin of theworkpiece.

A somewhat similar system may be used to obtain Y-coordinateregistration of the sweeping laser spot to the circuit pattern of theworkpiece, but in this instance using a data signal voltage data signalsfrom the horizontal registration lines 78A, 78B, 78C (FIG. 17) in theleft and right margins of the workpiece(s) 1, together with other datasignals, are sent on the cable 253 to the comparator 254. The datasignals are sent on cable 266 to the gate section 243 where the datasignals from the left margin horizontal registration lines aresegregated from other data signals and returned to the comparator 254 oncable 267. Likewise the data signals from the right margin horizontalregistration lines are segregated and returned to the comparator 254.The horizontal registration lines are sufficiently long (e.g. 0.030inches) such that a stable voltage measurement may be taken from thesegregated left and right margin data signals. Such voltage measurementsare then compared to standardized white and/or dark voltage signalswhereby the relative overlap of the sweeping laser spot on white and/ordark horizontal registration lines may be used to generate suitablesignals that are proportional to such overlaps. Such overlap signals arepower and/or voltage amplified and transmitted by means of cable 292 tosuitable flexible prism actuators 293. Thus segregated data signals fromthe left margin horizontal registration lines may thus be used bysuitable actuators 293 to apply vernier rotation to the left end of theflexible prism 33 and from the right margin horizontal registrationlines for vernier rotation to the right end of the flexible prism 33.Note that if the vernier rotations of the left and right ends of theflexible prism 33 are not identical and/or in the same direction of theflexible prism may be twisted. By such means the sweeping laser beampassing through the flexible prism 33 may be deflected by vernier prismrotations into Y-coordinate registration with the circuit line patternon the workpiece 1. This procedure may be repeated with horizontalregistrations located lower in the left and right margins of theworkpiece thereby periodically checking and/or improving theY-coordinate registration of the sweeping laser beam to the circuit linepattern. Additionally, in this instance, if the prism deflections aregreater than the manufacturing tolerances for a workpiece 1, theworkpiece may be rejected by a power amplified signal on cable 289 tothe accept, reject marker 70.

The data signals of circuit line patterns on cable 254 together withother data signals may be redirected through the comparator 254 to cable266 and the gate section 243 where the circuit line pattern data issegregated from other data. The segregated pattern data is returned tothe comparator 254 by cable 267. As previously selected and designatedby the workpiece part number, the correct image data in the correct datamemory bank 244 responds to X and Y coordinate addressing by laser spotpositional data on cables 246, 249. At any such addressed X and Ycoordinate the correct image data provides either a white or a darksignal for that address and the data signal is transmitted to thecomparator 254 by means of cable 294. The comparator 254 then comparesthe segregated circuit pattern signal on cable 267 with the white ordark signal from the correct image data on cable 294. Then if a whitecircuit pattern signal is in agreement with a white correct data imagesignal and/or a dark circuit pattern signal is in agreement with a darkcorrect data image signal the portion of the circuit pattern at the X, Yaddress being inspected by the sweeping laser spot is assumed to becorrect. However, if a white pattern signal occurs in disagreement witha dark correct data image signal, or vice versa, there may be apotential defect in the circuit pattern at that X, Y coordinate addressthat requires further evaluation before accepting or rejecting theworkpiece. To effect such an evaluation a white error signal or a darkerror signal is transmitted by cable 297 for storage in an error section296 of the memory bank 244 while concurrently the X, Y coordinateaddress of the error on cables 246, 249 is also stored therein. Theblack or white error signals are also transmitted by cable 264 to thecomputer 256 where a miniprogram is initiated to determine the extentand hazard of the error and/or subsequent errors at contiguous X, Ycoordinate addresses. The cables 257, 258 transmit error data betweenerror section 296 and the computer 256 whereby the mini-program maydetermine that white errors extending half-way or more across a darkconductor line are potentially hazardous electrical open circuits to berejected, and/or that dark errors extending half-way or more betweenadjacent conductor lines are potentially hazardous electrical shortcircuits to be rejected. Rejection signals from the mini-program aretransmitted by cable 264 to the compressor 254 for power amplificationand to accept or reject marker 70 by cable 289. If all circuit patterndata is in agreement with the correct image during the inspection of theworkpiece and no potentially hazardous errors have been found thecomparator generates and power amplifies an accept signal that istransmitted to the accept or reject marker 70 by cable 289.

When a workpiece 1 is rejected for any course such as dimensions,errors, etc. rejection data including type of rejection and/or error,the X, Y coordinate address of the error, and part number are stored inthe error section of the memory bank 244. Then if another sequentialworkpiece of the same part number has the same error at the same addresslocation, the computer 256 may be programmed to issue a warning signalon cable 272 that includes the rejection data. It is probable that thenext corresponding workpiece may include the same course for rejectionand that diagnostic and/or corrective action may be required eariler inthe production line processing. Thus rejection data on cable 272 may besent to a remote location where such data may be used to save valuablediagnostic time by automatically positioning a microscope over therejection area address on a corresponding workpiece. The cable 272 mayalso be used to send various production control data that is availablefrom the inspection tool system to a remote production control computersystem.

DATA HANDLING, PROGRAM

In order to obtain a maximum production throughput of workpieces, fromthe inspection tool equipment the highest practical speed of the laserinspection components preferably should not be limited by the highestpractical speed of the data handling components and vice versa. Also theinspection tool's correct data memory bank and computer preferablyshould be limited to economically practical sizes. The size and/orcapacity of the memory bank may be reduced by data compression but datacompression may also increase the effective size of the computer.

Three data memory bank and computer systems are described below, inwhich the second and third systems use various methods for datacompression. Data bits, data bytes, data addresses, and data numbersetc. may be herein described generically as data points.

The first system is essentially a one-to-one system with no datacompression. In such a one-to-one system the memory bank stores completeand correct image data for one or more workpiece(s) with the datapreferably being automatically selected and designated by the workpiecepart number. Within the stored correct image data a white or dark signalis stored for each X, Y address point and when suitably addressed bydata from sweeping laser spot on the grating each such address point mayissue a white or dark signal for comparison to correspondinglypositioned data from the workpiece(s). This if a 6.000 inch by a 6.000inch workpiece were to be inspected at 0.001 inch X and Y incrementsthere would be 6000 × 6000 = 36,000,000 X, Y addressable data points inthe correct image data for each workpiece part number. Considering thatthere may be as many as 100 or more different part numbers a very largecorrect data memory bank may be required to provide high speed access to100 × 36,000,000 = 36,000,000,000 X, Y addressable data points. However,this system may use a relatively small computer.

The second system may use data compression for X-coordinate data. For anexample of such data compression a dark circuit conductor line 1.000inch long horizontally in the X-coordinate and 0.006 inches widevertically in the Y-coordinate may be used. With the left to rightsweeping laser spot X, Y registered to the circuit pattern the sweepinglaser spot may first encounter a white or dark transition at the 0.006inch vertical width of the dark circuit conductor line. The X, Y addressof this first transition from white to dark is in the memory bank ascorrect image data and a dark signal is issued for comparison to worksheet data which should also provide a dark signal. However, in thisinstance, for data compression purposes, the white to dark transitionsignal from the correct image data activates a dark signal latch circuitin the comparator that stays latched and continues to issue dark signalsfor the next 99, X, Y coordinate addresses of the 1.000 inch long darkline to the right of white to dark transition signal. Since such latchcircuit issue dark signals are the equivalent of correct image datasignals the latter need not be included in the correct data memory bankand data compression thereby accomplished. The dark signal circuit stayslatched until the sweeping laser spot traversing the dark lineencounters the end of the dark line and a dark to white transitionlocation. At this location and X, Y address the correct image datashould issue a white signal for workpiece data comparison purposes. Thiswhite signal unlatches the dark signal latch circuit and latches a whitesignal latch circuit in the comparator that stays latched and issueswhite signals at consecutive X, Y coordinate addresses until a darksignal is received to unlatch the white signal circuit and latch thedark latch signal circuit, etc. In using this data compression systemonly the X, Y coordinate addresses of white to dark and dark to whitetransitions are required to be addressable and maintained in the correctmemory data bank thereby accomplishing a data compression of about 95%for dense circuit patterns. Thus relative to the previously describedsystem No. 1 only about 0.05 × 3,600,000,000 = 18,000,000 addressablememory points may be required for about 100 different workpiece partnumbers in a large memory bank.

A third system may use a smaller memory bank and a larger computer fordata compression by generating correct image data from a memory bankpart number program and a moderate quantity of memory bank "characters."If the original circuit pattern designer has followed the "ground rules"the 6.000 inch by 6.000 inch square of the workpiece being inspected maybe thought of as being covered by an orthogonal matrix of small 0.012inches by 0.012 inches square areas, hereinafter called characters. Thefour edges and the centers of such small square characters may alignwith a 0.006 inch by 0.006 inch X, Y matrix grid line pattern occurringfrom and used as the original pattern design reference matrix but notactually present on the workpiece being inspected. The circuit conductorlines, conductor filled via holes, etc. are "centered" on X, Y gridlines of the 0.006 inch X, Y matrix grid that pass through the centersof the small square character areas. Thus if a complete circuit patternwere to be cut (not actually) into the small square characters describedabove like pieces of a puzzle, and mixed up, each square character wouldretain a portion of the pattern and the complete circuit pattern couldbe reassembled, but with difficulty, from the square character pieces.However, if each character piece were to have a microscope readablenumber, and the puzzle assembler were to have a code sheet providingcharacter numbers for a reassembly sequence for the puzzle, the completepattern could be reassembled rapidly. The above puzzle analogy mayprovide an oversimplified description of the No. 3 system of datacompression but may illustrate the principles involved in practicalapplications of the system. A square circuit pattern area 6.000 incheswide and 6.000 inches high may have 6.000/0.012 = 500 character areas inwidth and height or a total of 500 × 500 = 250,000 character areas in acomplete circuit pattern, or for 100 part numbered workpieces 100 ×250,000 = 25,000,000 character areas. However, by arranging differentindividual characters in different sequences and/or locations only about50 different characters may be required to complete a circuit pattern.An analogy for this is a typewritten page where only about 75 capitaland small letters A to Z punctuation marks, and decimal numbers 0 to 9may be typed in different sequences and/or locations to fill a page, or100 pages.

As described previously the character areas are 0.012 inches by 0.012inches square with reference vertical and horizontal center lines of the0.006 inch X, Y reference grid matrix intersecting at the centers of thecharacter areas. The character areas include a 0.001 inch X, Y referencesub-grid and thus there are 12 × 12 = 144 sub-grid areas each of thelarger character area. Each 0.001 inch square sub-grid area in eitherwhite or dark according to the pattern configurations that may berequired to form individual characters in the larger (0.012 inch square)character area. A few examples of individual character patterns aredescribed below and assigned sequential numbers

(01), (02), (03) etc.:

(01) An all white character area

(02) An all dark character area

(03) A white area with a vertical 0.006 inch wide dark line areacentered on the vertical center line.

(04) A white area with a horizontal 0.006 inch wide dark line centeredon the horizontal center line.

(05) The pattern of (03) above with a dark horizontal 0.006 inch widestub line extended to the right and centered on horizontal center line.

(06) The pattern of (05) above except that the dark stub line isextended to the left.

(07) The pattern of (04) above with a dark vertical 0.006 inch wide stubline extended upward and centered on the vertical center line.

(08) The pattern of (07) above except that the dark stub line isextended downward. (09) The patterns of (03) and (04) above combined toform an intersection cross.

(10) A white area with an L shaped dark configuration comprising a darkvertical line 0.009 inches long and 0.006 inches wide extending from thetop of the square downward that is centered on the vertical line, with a0.006 inch wide dark stub line extending to the right that is centeredon the horizontal center line.

(11) The configuration of (10) above rotated 90° clockwise about itscenter point.

(12) The configuration of (10) above rotated 180° clockwise abouts itscenter point.

(13) The configuration of (10) above rotated 270° clockwise about itscenter point.

(14) A white area with a centered 0.007 inch diameter dark circle (viahole cap). In this instance the curvature of the circle may be simulatedby white and/or dark 0.001 inch sub-grid squares and/or sub-grid squaresin which about 40% of the square area is white and/or dark. Such 40%squares preferably should be provided for by including special data inthe correct image data for comparison of photocell voltage responses.

(15) The configuration of (14) above with a 0.006 inch dark stub lineextending to the right and centered on the horizontal center line.

(16) The configuration of (14) above rotated 90° clockwise about itscenter point.

(17) The configuration of (14) above rotated 180° clockwise about itscenter point.

(18) The configuration of (14) above rotated 270° clockwise about itscenter point.

(1) to (18) Notes: Substantially all 6.000 inch by 6.000 inch squarecircuit line conductor patterns may be assembled from combinations ofthe above described characters. Ground plane and voltage plane conductorpatterns may require additional characters. If permitted by the "groundrules" other additional characters may be included for various diagonalline patterns. A 6.000 inch by 6.000 inch matrix of various charactersmay be assembled from data stored and addressable by the workpiece partnumber. Such stored data may include an X, Y coordinate address for thecenter of each character and the characters configuration referencenumber (-). Since there would be 500 horizontal line of X-coordinateaddresses and 500 vertical lines of Y-coordinate addresses for thecharacters in the matrix of characters there would be a total of 500 ×500 = 250,000 X, Y coordinate addresses for the characters of eachworkpiece, or 25,000,000 addresses for 100 different workpieces. Thedata configuration of each individual 0.012 inch by 0.012 inch charactermay be permanently stored in the correct image data memory bank as 12 ×12 = 144 correct image data points, and when suitable addressed by itsconfiguration number (-) and its X, Y address make such data availableat the X, Y address. Since there may be 50 different characters thecorrect memory data bank may require permanent storage for 50 × 144 =7200 addressable data points which may be additive to 25,000,000addresses for 100 part numbers previously described.

A computer program for assembling the characters of each 6.000 inchsquare circuit pattern should preferably assemble the characters insequential horizontal rows of contiguous characters starting from theleft margin of the workiece. Thus a contiguous horizontal of rows of 50such characters would be in an area 6.000 inches wide (X-coordinate) and0.012 inches high (Y-coordinate). The computer assembling program shouldalso include means whereby the data points stored as 0.001 inchsub-matrix data in contiguous horizontal rows of such contiguouscharacters 6.000 inches wide (X-coordinate) and 0.001 inches high(Y-coordinate) may provide X, Y addressable sub-grid correct image datapoints sequentially and continuously from the left to right margins ofthe ciruit conductor pattern. Additionally, the computer program mayinclude means whereby two horizontal rows of contiguous characters maybe used on an alternating basis; a first horizontal row of previously"set up" contiguous characters being addressed for sub-grid correctimage data while concurrently a second horizontal row is being set upwith contiguous characters by the workpiece part number program. Afterthe addressing of the first row is completed, addressing is switched toaddress the second of contiguous characters and the program erases thefirst row program. Concurrently with the addressing of the second row ofcontiguous characters the first row is being set up with contiguouscharacters by the workpiece part number program, its next designatedY-coordinate row of contiguous characters. After the addressing of thesecond row of contiguous characters is completed, addressing is switchedto the first row and so on until the addressing of correct image datapoints is completed for a 6.000 inch by 6.000 inch circuit pattern.

After the automatic reading of the workpiece part number in the leadingedge margin of the workpiece this system for data compression providesabout 36,000,000 correct image data points for each different workpiecepart number, but data for 100 such part numbers requires only about25,000,000 memory bank stored data points. This represents a datacompression factor of about 144 when compared with about 3,600,000,000uncompressed data points required for 100 workpiece part numbers.

OPERATION OF THE INSPECTION TOOL

The overall operation of the laser beam inspection tool will bedescribed in terms relative to previous component descriptions. Theoverall operation may include a number of sequential sub-operations:

1. Loading the inspection tool with a workpiece or a long web orworkpieces, manually setting adjustments to compensate for grossshrinkage and/or expansion of the workpiece, manufacturing tolerancesetc. if required, whereby the nominal workpiece dimensions areestablished, and starting up the tool's inspection operations.

2. As a workpiece passes through the narrow inspection zone the tool mayidentify the workpiece part number, job lot number, day code number,shrinkage and/or expansion numbers, etc.

3. Informing the computer of the inspection tool relative to dataacquired in 2 above whereby the computer selects a correct inspectionprogram from its data bank and/or generates a corrected program bycomputation.

4. If further gross adjustments for shrinkage or expansion may berequired based on data from 2 above, nominal workpiece dimensions may berestablished by automatically adjusting the position of the grating byusing its position seeking motor, and automatically changing therotational speed of the workpiece cylinder.

5. With the grating and the flexible prism in nominal positions(actuators not energized) the upper left and right registration patternsmay be inspected for dimensional data.

6. The workpiece may be rejected if dimensions from 5 above may exceedthe nominal dimensions including manfacturing tolerances by applying arejection symbol in the right margin of the workpiece in line with therejection defect. This may be applied in any conventional manner, suchas a printing wheel, ink jet etc.

7. If the dimensions from 5 above differ from the nominal dimensions ofthe workpiece but are within acceptable manfacturing tolerance limits,suitable voltages will be automatically applied to the actuators of thegrating and the flexible prism whereby vernier adjustments are made todeflect the sweeping laser beam spot from its nominal positions and intoregistration with a suitable inspection matrix grid which corresponds tothe actual circuit pattern dimensions of the workpiece.

8. Inspection of the circuit pattern area on the workpiece for correctpattern dimensions and potential electrical short and/or open circuits.

9. When defects in circuit pattern dimension errors are found in 8above, the computer will compare such errors with allowable dimensionaltolerance limits and if excessive may reject the workpiece. Thus anominally dimensioned workpiece with a small dimensional error may beaccepted whereas another workpiece having dimensions near the limit ofmanufacturing tolerances may have an error in the wrong directionsufficient to cause rejection. When rejected, a rejection symbol may beplaced in the right hand margin in line with the rejection defect.

10. When a potential short and/or open circuit is found in 8 above, thecomputer may analyze the extent of the short and/or open circuit. Thismay involve data from several successive sweeps of the laser spot toreveal continguous defects extending from one circuit line conductor toanother conductor causing the workpiece to be rejected, whereas if thecontiguous short circuit defects stop at 0.003 inch or more from anotherconductor, the workpiece may be accepted. Similarily if contiguous opencircuit defects extend across a 0.006 inch wide circuit line conductorthe workpiece may be rejected, whereas if the open circuit defectsextend into the conductor 0.003 inch and are no wider than 0.006 inchthe workpiece may be accepted. When the workpieces are rejected forshort and/or open circuits a rejection symbol may be placed in the righthand margin in line with the defect.

11. Periodically spaced additional registration patterns may be placedin the left and right margins from the bottom of the workpiece. Suchregistration marks may be used to correct the registration of thesweeping laser spot using a procedure similar to that described in 7above.

12. After completing the inspection of the circuit pattern area of thegrating and the flexible prism may be returned to their nominalpositions (actuators not energized) and the lower left and rightregistration patterns may be inspected for dimensional data.

13. The workpiece may be rejected if dimensions from 12 above exceed thenominal-dimensions including manufacturing tolerances by applying arejection symbol in the right margin of the workpiece in line with therejection defect.

14. The succeeding workpiece may now be manually or automatically fedinto the inspection zone of the inspection tool and the sub-operations 2to 13 above may be repeated. Note that this next workpiece may have adifferent part number, circuit pattern, etc.

15. If desired, when two or more successive workpieces having the samepart number have similar rejection defects located in substantially thesame position, a warning signal may be issued to the inspection tooloperator. The warning signal may appear on the tool's control panel as avisibly readable part number with the X and Y coordinates of the defect.This provides a convenient means for locating the source of the defectin previous processing operations before inspection.

16. The computer may also conveniently provide a production control datafor workpiece such as the quantity of various part numbers accepted,throughput rates, rejection rates, day codes, job lot numbers, etc.

COMPARISONS OF INSPECTION FUNCTIONS

While accuracy and cost effectiveness may be the prime overallobjectives of a mechanized inspection tool it may be understood thatnumerous trade-offs between accuracy and cost have been consideredduring the evolution of a preferred and/or optimum design. Some of theproblems involved in an unused earlier design are shown in FIG. 33A.Below it in FIG. 33B, for comparison purposes, are the results ofsolving the problems with the preferred and/or optimum design describedheretofore and that provides greater inspection accuracy and speed at alower cost. As used herein the drawing of FIGS. 33A and 33B employduplicate numbers but with the suffix A applying to the unused earilerdesign and the suffix B applying to the preferred design.

Horizontal conductor lines 226A, 226B may interconnect with verticalconductor lines 227A, 227B near the upper left corner of theworkpiece(s) 1 with the white-to-dark external edges of the conductorlines being 230A, 230B and 231A, 231B respectively. Similarly horizontalconductor lines 229A, 229B may interconnect with vertical conductorlines 229A, 229B near the lower right corner of the workpiece(s) 1 withthe white-to-dark external edges of the conductor lines being designated232A, 232B and 233A, 233B respectively. As shown in FIGS, 33A, 33B theconductor lines may be 0.006 inches wide and a large central portion ofthe worksheet(s) 1 is shown broken away by the diagonal break lines sothat only the remaining corner portions are shown. For dimensionalreference purposes "datum lines" for Y=0.000 and X=0.000 may coincidewith the top line and the left line of the circuit pattern outlines 50Aand 50B respectively.

In the eariler design it was proposed to use 28,000 laser sweep linesper revolution of the cylinder 9 (FIG. 1) wherein a 0.001 inchY-coordinates sweep line grid might be obtained; i.e., 4 sheets of b 7 ×7 inch material with workpiece 1 centered in the sheets, 7 × 4 = 28inches per revolution of the cylinder. A problem then evolved inobtaining 0.001 inch inspection measuring increments along the sweeplines for X-coordinate measurements. The problem is that the position ofthe focused laser spot on the worksheet may be a tangent of the angle24-26 (FIG. 3) function, and the sweep velocity is a square function ofthe secant of the angle. The problem might have been partially correctedby adding a large negative lens system to the laser optics for tangentcompensation but inspection accuracy might be impaired. A bettercorrection approach might be to have the computer interpret the angleand calculate suitable secant function compensations.

Also in the earlier design it was proposed to use an average sinteringshrinkage factor of 0.828 whereby the X and Y inspection dimensionscould be expanded by calculation from the sintered design dimensions.Thus, for example, in FIG. 33A if the sintered design dimensions for thedark edge lines 230A, 231A were each 0.0025 inches from their respectiveX and Y datum lines their inspection dimensions may be 0.0025/0.828 =0.003019 inches or 3.019 scan lines or scan line increments from theirrespective X and Y inspection datum lines. Likewise if the dark edgelines 232A, 233A were each 4.9975 inches from their datum lines in thesintered design their inspection dimensions would be 4.9975/0.828 =6.035628 inches or 6935.628 scan lines or increments from theirinspection datum lines. Similarly the 5 × 5 inch sintered dimensions ofthe circuit pattern outline may be expanded to 6.038647 × 6.038647inches for scan line and/or increment counts of 6038.97 × 6038.647 forinspection purposes. This introduced problems of how to cope withinspection dimensions such as 3.019, 6035.628, 6038.647 scan linesand/or increments since the computed data may include decimal pointswith significant data to the right of the decimal points. Also sinceonly integer scan lines and/or increments may be readily counted todetermne line and/or circuit pattern positions, other problems andinaccuracies could be introduced by not using or rounding but the datato the right of the decimal point.

Likewise in the earlier design it was believed that up to a ±0.0005 inchmechanical registration error between the workpiece sprocket holes 3(FIG. 1) to the sprocket pins 12 might be within adequate accuracylimits for inspection purposes. Thus the upper dark edge lines 230A,230B and 231A, 230B might be 0.0005 inch higher and to the left of itscalculated position. However if the workpiece also has a 0.001-inchpre-inspection shrinkage that was cumulative to the registration erros,then the lower dark edge lines 232A, 232B and 233A, 233B wold be 0.0015inches higher and to the left of calculated positions.

Of the complete laser raster scan pattern only portions of 3 upper lasersweep lines 234A, 235A, 236A and 1 lower sweep line 237A are seen inFIG. 33A. If the sweep lines and their X-coordinate increments have beenaccurately registered to the inspection tool previously, the incrementsalong the sweep line 234A will be entirely on white areas and thephotocells 36 (FIG. 1) may readily recognize white signals. The whitesignals may then be compared with correct white data image for theincrements in, for example, the computer memory bank and the photocellsignals accepted as being correct. The next sweep line 235A mayencounter problems since the dark edge lines 230A, 231A may be .0005inches higher and to the left of where they should be due to mechanicalregistration errors of the workpiece 1A. Thus some increments of thesweep line 235A may be half on white and half on dark while the correctdata image may be for white increments only and consequently theinspection process may become confused. Similar confusion may begenerated as the upper sweep line 236A traverses the vertical dark edgeline 231A since an increment can straddle the line and a half white halfdark signal may result for that increment. Likewise, confusion mightoccur for increments having 10% to 90% white or dark area. One alternateto confusion might be to call a confused increment either all white orall dark; and thus allow an error up to 0.0009 inches, which error mightbe cumulative with other errors. Another alternate might be to disregardconfused increments and not compare them with correct image data whichmight allow similar errors. Voltage interpolation of confused incrementdata might be used to determine pattern line locations but this mightrequire additional time for voltage stabilization and measurement foreach of the 36,000,000 or more increments and slow down the inspectiontool to an unacceptable low speed. As previously described, the darkedge line 232A in the lower corner may be 0.0015 inches higher than itshould be due to cumulative errors and thus a portion of the lower sweepline 237A which should be totally within the dark circuit line 228A missthe circuit line entirely. An analysis of skewed patterns (FIGS. 14, 15,16) indicated that further errors were possible. If all the errors wereto be cumulative in a wrong direction the sum of the errors could benearly 0.003 inches, which may be unacceptable for inspection purposes(depending upon line thickness, pattern density etc.), thus indicatingthat a different design approach is required.

Some of the accomplishments of the different and preferred designapproach are illustrated in FIG. 33B. In the preferred design theX-coordinate laser sweep lines and their 0.001 inch X-coordinateincrements are registered to the circuit pattern of the worksheet 1rather than having the sweep lines and increments registered to a fixedelement of the inspection tool. This is accomplished by adding easilyrecognizable and standardized registration patterns in the margins ofthe workpiece(s) 1 adjacent to the circuit pattern outline area 50. Thenby making accurate measurements between the left margin registrationpattern and the right margin pattern registration pattern the upper leftand right corner locations of the circuit pattern outline 50 may bedetermined since there is a standardized or predetermined dimensionbetween the registration patterns and the circuit pattern outline 50. Tomake accurate measurements, the partially reflecting mirror 27 (FIG. 1),the grating 28, the lens 31, and the photocell 32 were added to theearlier design whereby the position of the laser spot on the workpiececould have a duplicate spot position on the grating for generating 0.001inch X-coordinate increment signals and for measurement purposes. Aftermaking the measurements between the registration patterns, measurementdata from the left registration pattern are converted into suitablevoltage signals and applied to the grating actuators 115, 117 (FIG. 21)thereby moving the grating slightly left or right to bring the gratingpattern into registration with the registration pattern and the circuitline pattern. Since the grating pattern generates the 0.001 inchX-coordinate increments used for measurement purposes the grating "datumline" may now be registered to the "datum line" circuit line pattern.The effect of such X-coordinate registration may be seen in FIGS. 33Band 32. The preferred effect of such registration is that the laser spot221 (FIG. 32) is entirely on a white area and the next laser spot 223 isentirely on a dark area with a vertical line such as 224 being mutuallytangent to both spots. Portions of the laser sweep lines 235B, 236B(FIG. 33B) show the vertical line 231B mutually tangent to white anddark laser spots. Thus for the upper left corner of FIG. 33B thephotocells 36 (FIG. 1) respond only to white spots or dark spots whencomparing signals with the image data in the computer memory bank and nointerpolation or data omission may be involved. Similarly the ±0.0005mechanical registration error of FIG. 33A may be avoided by theregistering the X-coordinates of the laser sweep pattern to theworkpiece pattern. Also the grating, in providing dimensionally stable0.001 inch increments, avoids repetitive computer calculations thatotherwise would be required to compensate for tangent and/or secantfunctions of the angle 24-26 (FIG. 3) thereby saving computing time.

Registration data for the Y-coordinate may also be obtained from theleft and right margin registration patterns. The white-to-dark anddark-to-white horizontal edges of the registration lines 78A, 78B, 78C(FIG. 17) of the patterns are long enough (0.030 inches) to providevoltage stabilization for interpolation measurements if the sweepinglaser spot 205 (FIG. 31A) should straddle a horizontal edge such as line206. The interpolation data may be translated into voltage and appliedto the actuators of the flexible prism 33 (FIGS. 1, 2, 3, 29). When soactuated, the sweeping laser beam 25 may be deflected by the flexibleprism 33 and brought into Y-coordinate registration with the circuitpattern. After registration the Y-coordinates of the sweeping laser beamspots should preferably be such that the laser spots are tangent to ahorizontal line as shown in FIGS. 31B, 33B. In FIG. 31B a spot 234B, maybe entirely on a white area and a spot(s) 235B, may be entirely on adark area with a horizontal line 230B mutually tangent between thespots. Thus after registration the photocells 36 (FIGS. 1, 29) respondto only white or dark signals for comparison of data images in thecomputer memory bank and no interpolation is required as in FIG. 33A.The registration of the Y-coordinate sweep lines to the workpiece 1rather than to a fixed element of the inspection tool thus avoids±0.0005 inch mechanical registration errors, interpolations, and alsoaccommodates Y-coordinate portions of skewed circuit patterns such as inFIGS. 14, 15, 16.

The expansion of the sintered design pattern dimensions of the workpiece1 to the larger inspection pattern dimensions present decimalinterpolation problems for a large portion of the Y-coordinate sweeplines and their X-coordinate intervals. After the X and Y registrationat the upper left corner of the workpiece 1, FIG. 33B, the upper leftline portions may be used as a datum line 50B for dimensional referencepurposes. Thus an X or Y sintered coordinate of 0.9925 inches mightbecome 0.9925/0.828 = 1.19867 inches for inspection purposes, or 1198.67scan lines or increments, and the number 0.67 to the right of thedecimal point may require interpolation. A similar expansion of thesintered 5.000 dimensions of the outline 50B, 5.000/0.828 = 6.03847inches or 6.038.47 scan lines or increments.

The method for avoiding interpolation by the 45°reference lines of thegrating provides integer numbers for the increments along the lasersweep lines as the laser sweeps across circuit line edges on theworkpiece 1. It was noted that in the sintered design pattern the 0.005inch wide circuit lines were centered on a 0.005 inch X and/or Y matrixdesign grid and the edges of such lines coincided with a 0.0005 inch Xand/or sub-grid. Thus the centers of such lines might have X and/or Ycoordinate addresses such as --5.0 or --0.0 with the last two digitsbeing either 5.0 or 0.0 and where a - may be any number from 0 to 9.Likewise the edges of 0.005 inch wide lines centered on the 0.005 inchmatrix grid have line edges 0.0025 inches offset from the center linesand would have addresses such as --2.5 or --7.5 with the last digitsbeing 2.5 or 7.5. To obtain expanded inspection addresses with integernumbers the sintered design numbers may be multiplied by a factor of 1.2rather than being divided by the shrinkage factor 0.828: such as --2.5 ×1.2 = --3. and 5.000 × 1.2 = 6.000 rather than --2.5/0.828 = --3.0193and 5.000/0.828 = 6.038547. Note that multiplying by 1.2 providesinteger address numbers with small dimensional errors and that dividingby 0.828 provides correct dimensional numbers that may include a decimalpoint and that the numerals to the right of the decimal point mayrequire interpolation. However, by rotating the grating with its 45°reference lines about its pivot point at the X "datum line" by its motor132 (FIG. 21) the length of the laser sweep line across the 6000 gratinglines may be increased from 6.000 inches to 6.038647 inches while stillretaining 6000 lines or X-coordinate increments between the 0.0 inch"datum line" and the 6.038647 inch dimension. Thus the gratingincrements may be registered to the vertical line edges of a circuitpattern having a "nominal" shrinkage factor of 0.828. SimilarY-coordinate registration may be accomplished by increasing therotational speed of the cylinder 9 by the stepping motor 179 (FIG. 30)whereby 6000 sweep lines may be spread over a "nominal" dimension of6.038647 inches as previously described. Accommodation and registrationfor other "nominal" dimensions resulting from sintering shrinkagefactors other than 0.828 may be similarly accomplished.

An X and/or Y pre-inspection shrinkage and/or expansion factor of ±0.001inch relative to "nominal" dimensions may be accommodated forregistration purposes by accurately positioning eight or moreperiodically spaced registration patterns in the left and right marginsof the workpiece 1. Such periodic registration patterns may be used toperiodically apply correction signal to the actuators of the grating andthe flexible prism as the workpiece 1 progress through the inspectiontool. Thus the laser sweep line 237B (FIG. 33B) and its increments maybe suitably registered to edge lines 232B, 233B in the lower rightcorner of the circuit line pattern as shown.

In the preferred method the combined result of registering the laserraster scan pattern to the workpiece circuit pattern as described abovemay be that each increment of a laser sweep line sees only entirelywhite areas or entirely dark areas and no precise interpolations of lineedge positions is required for the inspection of an acceptable "nearperfect" workpiece. By avoiding precise interpolation inspection speedis significantly increased. However, in a workpiece that may be otherthan "near perfect" there may be occasional errors attributable to outof position edges of circuit lines and via hole caps or random edges ofpossible electrical short and open circuits, etc. Such errors may bepresent if a white and/or dark line edge may be within a laser scan linespot increment when a correct spot should "see" either entirely white ordark increment areas. Approximate photocell voltage measurements of sucherrors rather than a precise interpolation of line edge positions areadequate for inspection "accept" and/or "reject" purposes and permit anincrease in inspection speed. In a well registered circuit pattern thedesign may be such that if a white increment spot area were to slightlyintrude into what should have been on entirely dark increment spot areasuch that the photocell response voltage, without time for completevoltage response stabilization, might be only 1/4 or less above the darkresponse level, the dark increment spot may be "accepted." Likewise if adark increment spot area were to slightly intrude into a white incrementspot area the white voltage response might be reduced by only 1/4 orless and the white increment spot may be "accepted."However if thevoltage increases or reductions from such intrusions were to be 1/3 ormore the workpiece may be "rejected". The difference between 1/4 voltage"acceptance"and 1/3 voltage "rejection" may be used as an intermediate"guard band" where either "accept" or "reject" events occur due toelectrical noise levels, approximate photocell voltage level responsesand/or second order mechanical errors, etc.

Thus in overall summary, the reduction of cumulative errors in thepreferred configuration of the inspection tool may allow an inspectionaccuracy considerably smaller than ±0.001 inch over a 6 × 6 inch squarecircuit pattern area of a workpiece(s), and complies with the stacking,laminating, and sintering constraints previously described relative toFIG. 9.

Although the invention has been described with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts and the modeof operation may be made without departing from the spirit and the scopeof the invention as hereinafter claimed.

What is claimed is:
 1. An inspection tool comprising: means to feed aworkpiece to be inspected into a work zone, said workpiece having apattern to be inspected; a source of coherent light and means to effecta sweep of said coherent light across said work zone; first lightdetector means positioned adjacent said work zone to receive lightreflected from a workpiece in said zone from said sweep of coherentlight; an elongated flexible prism mounted for rotation adjacent saidwork zone and in the path of said sweep of coherent light, intermediatesaid work zone and said source of coherent light; first and secondactuator means connected respectively to opposite ends of said flexibleprism; means to energize at least one of said first and second actuatormeans to effect rotation of at least said one end of said flexible prismupon said first light detector means detecting misalignment of saidworkpiece.
 2. An inspection tool in accordance with claim 1 wherein saidworkpiece to be inspected includes Y axis alignment marks thereof forindicating the position of said workpiece along an axis transverse tosaid work zone, and means responsive to said first light detector meansfor actuating said energizing means to effect registration of saidsweeping coherent light across said work zone with said alignment marksby rotation of at least said one end of said flexible prism.
 3. Aninspection tool in accordance with claim 2 including a pair ofupstanding frame members at opposite longitudinal ends of said prism;means for connected to said frame members for adjusting the position ofsaid prism transversely of said work zone.
 4. An inspection tool inaccordance with claim 2 including a pair of upstanding frame members atopposite longitudinal ends of said prism, shaft and bearing meansconnected to opposite longitudinal ends of said prism, connecting saidframe members thereto and along the longitudinal axis of said prism. 5.An inspection tool in accordance with claim 4 including means to gripsaid prism inboard of said frame members and adjacent thereto; an offsetportion of said gripping means, said first and second actuator meanseach comprising push-pull actuators connected to an associated framemember and connected to said offset portion to effect rotation of saidprism about its longitudinal axis.
 6. An inspection tool in accordancewith claim 2 wherein said means to effect a sweep of said coherent lightacross said work zone comprises a multi-facet mirror; means supportingsaid mirror for rotation in the intended path of the beam of coherentlight from said source of coherent light, and first drive means foreffecting rotation of said mirror.
 7. An inspection tool in accordancewith claim 6 including a gear train interconnecting said first drivemeans to said means to feed a workpiece into said work zone whereby saidmirror rotation is in synchronism with said means to feed saidworkpiece.
 8. An inspection tool in accordance with claim 1 wherein saidmeans to effect a sweep of said coherent light across said work zonecomprises a mirror; means supporting said mirror for rotation in theintended path of the beam of coherent light from said source of coherentlight, and first drive means for effecting rotation of said mirror. 9.An inspection tool in accordance with claim 8 wherein said mirrorcontains a plurality of facets.
 10. An inspection tool in accordancewith claim 8 including a gear train interconnecting said first drivemeans to said means to feed a workpiece into said work zone whereby saidmirror rotation is in synchronism with said means to feed saidworkpiece.
 11. An inspection tool in accordance with claim 8 includinglens means for focussing said sweep of coherent light into a beam.